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Geology and ore deposits of the Yukon territory Freshwater, Norman G. Morgan 1930

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GEOLOGY AND ORE DEPOSITS OF THE YUKON  A  TERRITORY  THESIS  Presented for the Degree of Master of Arts i n the Faculty o f Arts and Science at The University o f B r i t i s h Columbia by Norman G. Morgan Freshwater.  April,  1950.  CONTENTS  Introduction CHAPTER I Physiography CHAPTER I I General Geology CHAPTER I I I H i s t o r i c a l Geology CHAPTER IV Descriptive Geology Pro-Cambrian Palaeozoic Mesozoic Tertiary Quaternary and Recent CHAPTER V Igneous Rocks CHAPTER VI Economic Geology BIBLIOGRAPHY Plate I  Facing Page  P l a t e I I Facing Page  INTRODUCTION.  I n t h i s t h e s i s the w r i t e r has attempted to g i v e as complete a compilation o f the geology o f Yukon T e r r i t o r y , as the l i t e r a t u r e permits.  The geology o f  ' Yukon T e r r i t o r y i s lacking i n sedimentary formations and those sedimentary formations present have a rather remarkable s c a r c i t y o f i d e n t i f i a b l e f o s s i l remains. The work o f W.B* C o c k f i e l d and E+ Lees during the f i e l d season o f 1929 promises to straighten out at l e a s t some of the d i f f i c u l t i e s .  What information the w r i t e r has  o f these d i s c o v e r i e s has been stated i n the f o l l o w i n g pages* A discussion o f the placer deposits o f Yukon i s considered too extensive a subject to be d e a l t with i n t h i s t h e s i s and have thus purposely been omitted. Where p o s s i b l e and without going i n t o too much d e t a i l the w r i t e r has attempted t o c o r r e l a t e the g e o l o g y o f Yukon with that o f the I n t e r i o r o f  British  Columbia. A complete bibliography dealing with the l i t e r a t u r e published on the geology o f Yukon w i l l be found at the end o f t h i s t h e s i s .  Ftcjt.  " P h \ ) S t o g r o . p h t c . p3rovtuces of  the  YuKon  Yukon t e r r i t o r y i s e s s e n t i a l l y composed of three physiographic provinces which are continuous with similar d i v i s i o n s in B r i t i s h Columbia, to the southeast, and Alaska, to the west.  These physio-  graphic provinces named from southwest to northeast are: the Coastal system, the I n t e r i o r system and the Rocky Mountain system.  These three provinces form  the C o r d i l l e r a of North America. The C o r d i l l e r a extends from Mexico northward to the A r c t i c Ocean, p a r a l l e l i n g ,  to an amazing degree,  the P a c i f i c co^st l i n e of North America.  In British  Columbia the general trend uf the C o r d i l l e r a i s northwest, in Alaska the trend i s w e s t e r l y ,  <vhile in "Yukon  which i s in between, the course of the C o r d i l l e r a intermediate between the two, g e n e r a l l y  is  nort?webtrrly.  Lyin^ to the north, northeast, and east of the Rcc'.y Mountain system are various plains or lowland t r a c t s . - The A r c t i c Slope region, the Mackenzie l o w l a n f s , areas of broken wode3 ^ l ^ i n s , possibly belonging to the great p l a i n s . ( See Fig 1 . ) ^ ^ A. The Coastal System. The Coastal system, from the v i c i n i t y of the 50th to near the 60th p a r a l l e l , embraces only the ( 1 ) Cairnes D.D. — /Vhe^tcn D i s t r i c t , Yukon t e r r i t o r y , G.S.C. Mem. 31, P. 9.  Figure I I Nomenclature of the Mountains of Western Canada.  (2) Coast range. The Islands to the west were considered (1) by Dawson as a separate range and are now c a l l e d the i n s u l a r range by the Dominion Geographic Board.( See  (2)  F i g . 2)  The s i m p l i c i t y o f the Coastal system i s i n -  terrupted near the head o f Lynn canal, whence northward nad northwestward t h i s province embraces a number o f ranges o r mountain groups including the Coast range, the S t . E l i a s range, the Aleutian range and the Alaskan range, which are i n places separated by wide v a l l e y s . The Coast range c o n s i s t s , i n a general way, o f an i r r e g u l a r complex o f peaks and r i d g e s , that possess but l i t t l e symmetry other than a rough alignment p a r a l l e l to a northwesterly-trending a x i s .  The range  has everywhere a p r e c i p i t o u s and jagged aspect, and consists l a r g e l y o f k n i f e - l i k e c r e s t s , rugged or even n e e d l e - l i k e summits, and sharply i n c i s e d v a l l e y s .  The  summits i n southern B r i t i s h Columbia, r i s e to uniform a l t i t u d e s o f from 8,000 to 9,000 f e e t above s e a - l e v e l ,  .  but toward the north gradually decrease i n e l e v a t i o n , u n t i l i n Yukon they stand at only 5,000 to 6,000 f e e t ; though the change i n e l e v a t i o n i s apparently g r e a t , (ljDawson G.M.  it  "On the l a t e r physiographic geology o f the Rocky Mountain region i n Canada, with s p e c i a l reference to changes i n e l e v a t i o n and the h i s t o r y o f the g l a c i a l P e r i o d ; " Trans. Royal Soc. o f Can. V o l . V I I I See. I V . 1890, P. 4 . ( 2 ) Dominion Geographic Board o f Canada 1918.  i s so gradual as not to break the general uniformity o f summit-level which, however, bears no r e l a t i o n to structural features. The Coast range a f t e r f o l l o w i n g the coast l i n e from southern B r i t i s h Colombia t o near the head o f Lynn canal, passes behind the S t . E l i a s range, and thence northward, as f a r as i t extends i n t h i s d i r e c t i o n , c o n s t i t u t e s the most e a s t e r l y d i v i s i o n o f the Coastal system.  North o f Lynn canal, the Coast range  gradually becomes l e s s prominent, u n t i l i t merges i n t o the Yukon plateau i n the v i c i n i t y o f Lake Kluane at o o ' l a t i t u d e 61 and longitude 138 35. The Coast range has been considered by a  (1)  number o f g e o l o g i s t s  to represent a peneplanated o r  at l e a s t mature to o l d surface o f erosion.  Other  g e o l o g i s t s , however, maintain that t h i s terrane shows no evidence o f having ever been peneplanated.  (2) The Brooks,  S t . E l i a s range as the name i s aoplied by  with i t s broader s i g n i f i c a n c e , includes the  Chugach, Kenai, and Skolai mountains which are orog r a p h i c a l l y a western extension o f the S t . E l l a s range as t h i s term i s usually intended.  Thus d e f i n e d , the  S t . E l l a s range extends northwesterly from Cross sound, t l ) Dawson G.H. "Report on Kamloops map sheet, B.C." An. Rep. G.S.C. V o l . V I I . 1894 P.10B. Hayes, C.W. "An Expedition through the Yukon d i s t r i c t . " Nat. Geog.Nag. V o l . IV.P.128 ( 2 ) . B r o o k s , A.E. "The geography and geology o f Alaska." U.S.G.S. P r o f , paper #45 1906.  bends westerly near the mouth o f the Copper r i v e r , and near the head o f Prince William sound, i n longitude o 147, turns sharply southwest and merges i n t o the high(1) lands o f Eenai peninsula.  The St* E l l a s range v a r i e s  i n width from 50 miles near Cross sound, to nearly 100 m i l e s at Mount S t . E l i a s , and then narrows down to l e s s than 20 miles to the southwest i n the Eenai peninsula. This "range i s a rugged mountain mass p a r a l l e l with and close to the P a c i f i c coast from Cross sound as f a r as the entrance to Cook i n l e t , with one spur, the Skolai mountains, stretching t o the southwest.  On the sea-  ward aide, the range presents an abrupt escarpment, o f t e n r i s i n g d i r e c t l y from the water, while i t s northern slopes almost everywhere, f a l l o f f abruptly to the Central P l a t e a u . " (Yukon P l a t e a u . )  Peaks i n t h i s range  r i s e to great e l e v a t i o n s , f o r example Mt. S t . E l l a s and Mt. Logan which a t t a i n an e l e v a t i o n above the sea o f 18,024 and 19,500 f e e t  respectively.  Skolai mountains, o r more p a r t i c u l a r l y the Skolai-Natazhat Mountain group, which are l i m i t e d to the north f o r a distance o f approximately 40 miles by White River v a l l e y , are rugged i n character, with a l t i t u d e s o f 7,000 to 10,000 f e e t , and merge to the north o r northwest with the Wrangell mountains.  The most  prominent break through the mountain b a r r i e r or water(1J Brooks, A.H.  ^  Op. C l t .  (5) shed comprised o f Wrangell and Skolal mountains, i s known as Skolai pass, which l i e s between the heads o f Nizina and White r i v e r s . Wrangell mountains owe t h e i r o r i g i n to the accumulation o f v o l c a n i c material i n times so recent that the f o r c e s o f erosion have not y e t removed i t ; and they thus^ d i f f e r from the other ranges o f the Coastal system, which belong to that class o f the e a r t h ' s f e a t u r e s that are the r e s u l t of d i f f e r e n t i a l erosion i n regions of deformation and u p l i f t .  The highlands o f Wrangall  mountains possess the i r r e g u l a r forms t y p i c a l of v o l canic mountains which are b u i l t up dominantly o f lavas rather than ash d e p o s i t s . These mountains are, a l s o , exceedingly rugged end occupy an intermediate p o s i t i o n between Skolal and Chugach mountains i n the south and e a s t , and Nutzotin mountains on the northeast.  Mount Wrangell, with an  e l e v a t i o n o f 14,005 f e e t , i s c e n t r a l l y l o c a t e d i n the group o f mountains to which i t g i v e s i t s name, and a l though possibly the most imposing among them, i t i s not the h i g h e s t .  These mountains reach t h e i r culminating  point i n Mount Sanford which i s 16,200 f e e t above seal e v e l ; and at l e a s t f i v e other peaks r i s e to e l e v a t i o n s exceeding 12,000 f e e t .  The higher p o r t i o n s , o f  the  Skolai-Wrangell ranges c o n s t i t u t e a v a s t snow f i e l d from wi&eh scores of v a l l e y g l a c i e r s descend, and form  (6) the headwater sources o f p r a c t i c a l l y a l l the more important streams o f the r e g i o n . The Nutzotin mountains to the north, which are r e a l l y an eastern d i v i s i o n o f the Alaska range, are lowe r , but on the whole do not appear to be l e s s rugged than the Wrangell-Skolai mountains.  The average e l e v a t i o n o f  the highest summits o f the Nutzotin range i s from 6,000 to 9,000 f e e t , but t h i s range reaches i t s highest point i n Mt. A l l e n , which has an e l e v a t i o n o f 10,420 f e e t . Nutzotin mountains, however, include no extensive snow f i e l d s and t h e i r few g l a c i e r s are small and unimportant. B. Rocky Mountain System. The Rocky Mountain system extends northward from the western United States through Canada t o near the A r c t i c , where, south o f Mackenzie bay i t turns a l most at r i g h t angles, crosses the I n t e r n a t i o n a l Boundary, and continues in a d i r e c t i o n s l i g h t l y south o f west, across Alaska to the ocean.  South o f Yukon t h i s system  i s notably complex and includes s e v e r a l high ranges whose axes are i n general p a r a l l e l .  The Roeky Mountain  system o f Yukon has not been e x t e n s i v e l y explored and concerning i t r e l a t i v e l y l i t t l e i s known.  This t e r r a n e ,  however, constitutes a mountainous b e l t which stretches northward toward the A r c t i c and forms i n general the watershed between the Yukon r i v e r on the west and the Mackenzie r i v e r on the e a s t .  A f t e r bending to the south-  (7) west and entering Alaska this system i s known to be a complex mass and i s continued southwestward as a g r e a t trans-Alaskan chain to which the name Endicott mountains (1) has been applied* The Rocky mountains increase i n ruggedness northward from the 49th p a r a l l e l to Mt. Brown and Mt. Marehison where they a t t a i n t h e i r maximum h e i g h t s ; from thence northward they decrease i n ruggedness and e l e v a t i o n u n t i l where the Peace r i v e r crosses they resemble only r o l l i n g h i l l s .  T h e i r e l e v a t i o n v a r i e s from a  maximum o f 13,000 f e e t a t Mt Robson t o an e l e v a t i o n o f 6,000 f e e t where the Peace r i v e r c r o s s e s .  They have an  approximate width o f 200 miles i n the southern portion but t h e i r width decreases northwards.  The Rocky moun-  tains r i s e steeply from the Great Plains on t h e i r e a s t ern border, and on the west they are bounded by the Rocky Mountain t r e n c h — - the master v a l l e y o f the Cordilleras* The Mackenzie mountains, which include the g r e a t e r part o f the Rocky Mountain system i n Yukon, are  (2)  described by Keele  as a complex o f i r r e g u l a r mountain  masses which are the r e s u l t o f deformation and u p l i f t o f sedimentary rocks and include summits r i s i n g to t l ) Brooks A.H* ^The geography and geology of Alaska." U.S.G.S. Prop.paper #45,1906. PP 42-46 ( 2 ) Keele Joseph"A reconnaissance across the Mackenzie Mts. on the P e l l y , Ross, and Gravel r i v e r s , TRikon and N.W. T e r r i t o r i e s . " G.S.C, 1910 PP. 16-18  (8) heights o f 7,000 t o 8,000 f e e t above s e a - l e v e l . have a maximum width o f about 300 m i l e s .  They  The O g i l v i e  mountains appear to c o n s t i t u t e a northwesterly lobe o f  (I) the Mackenzie mountains.  The Mackenzie mountains are  bordered on the west by a northward continuation o f the I n t e r i o r system ( the Yukon Plateau } and on the east by the Mackenzie r i v e r and the Franklin mountains.  The  Mackenzie mountains are l e s s rugged than the Rocky mountains and o f g r e a t e r l a t e r a l  extent.  Throughout Yukon the axis o f the ranges comp r i s i n g the Rocky mountain system, have an echelon character, the d i f f e r e n t ranges not p e r s i s t i n g any g r e a t distance, but instead g i v i n g place i n e i t h e r d i r e c t i o n to other p a r a l l e l ranges. North of the Yukon r i v e r and just south of the  (2)  Porcupine r i v e r Cairns  describes the Keele mountains  as having undoubtedly had the seme physiographic h i s t o r y as the surrounding portion o f the Yukon plateau and they are considered to c o n s t i t u t e a portion o f t h i s t e r r e n e . " The Eeele mountains are characterized by deep canyonl i k e v a l l e y s , and the included, i n t e r - v a l l e y , l i k e upland areas*  plain-  The rugged, craggy, steeply  inclin-  ed v a l l e y walls r i s e abruptly f o r 1,500 f e e t o r more to ( 1 ) Cairns D-D. (2)Cairns D.D.  "The Yukon-Alaska I n t e r n a t i o n a l Boundary, between Porcupine and "Yukon r i v e r s Mem. 67. G.S.C. 1914 P.23. Op. c i t . P. 26.  (9) The upland above, and viewed from the edge o f one of these i n c i s i o n - l i k e drainage ways, the topography appears to be rugged i n the extreme.  When viewed from the up-  land, w e l l back from the v a l l e y w a l l s , a p l a i n - l i k e surf a c e i s presented with only occasional small, w e l l rounder summits r i s i n g above the general l e v e l .  Such  a nearly b a s e - l e v e l l e d or peneplanated and t y p i c a l l y old topography was apparently produced when the region stood much nearer s e a - l e v e l than at present.  In accord-  ance with t h i s assumption the p^anating process must have been^interrupted by a r e g i o n a l u p l i f t while occasi o n a l h i l l s s t i l l remained to r e l i e v e the monotony o f the former landscape, and these now c o n s t i t u t e monadnocks or residuals r i s i n g above the general plateau surface. The O g i l v i e Mountains are unusual in the f a c t that they are composed e s s e n t i a l l y of s o f t sedimentary rocks - - - mainly limestone.  The v a l l e y s and lowlands  are composed o f s l a t e s and schists which g e n e r a l l y are more r e s i s t a n t than limestones*  I n Yukon the extremes  o f temperature have more e f f e c t than the usual forms of erosion*  The s l a t e s and schists permit ready access o f  water,and f r o s t action i s prevalent to a high degree, thus the s l a t e s and schists s p l i t along the cleavage planes and r e a d i l y break o f f .  The f i n e - g r a i n e d  stone, on the other hand, does not permit the entrance  (10) o f water t o any g r e a t extent t h e r e f o r e f r o s t - a c t i o n on the limestones i s not as g r e a t on the s l a t e s and s c h i s t s . Thus the limestone forms the tops o f the mountain ranges in this v i c i n i t y . C. The I n t e r i o r System* The I n t e r i o r system o f Yukon, the Yukon Plateau, l a a continuation o f the i n t e r i o r plateau region o f c e n t r a l B r i t i s h Columbia.  I t i s cut o f f from the i n -  t e r i o r o f B r i t i s h Columbia by the Cassiar range which o occurs i n the v i c i n i t y o f l a t i t u d e 58 The Yukon plateau, comprises the major p o r t i o n o f the Yukon t e r r i t o r y and i s drained almost wholly o by the Yukon r i v e r .  I t extends from about l a t i t u d e 58  in  northern B r i t i s h Columbia, through Yukon and Alaska t o the Bering sea, and has a width o f from 200 - 400 m i l e s , s t r e t c h i n g from the ranges o f the Rocky Mountain system t o the inner members o f the Coastal system which f r i n g e s the P a c i f i c ocean* Into the upland surface o f t h i s plateau province i n Yukon, the main drainage courses have i n c i s e d channels varying from 5,000 to 4,000 f e e t i n depth, thus producing a v e r y i r r e g u l a r topography consisting essenti a l l y o f r o l l i n g uplands separated from each other by wide deep v a l l e y trenches.  The summits o f the unreduced  h i l l s and r i d g e s , l y i n g between the waterways, c o n s t i t ute remnants o f what was once, apparently, a g e n t l y  roll-  (11) ing p l a i n sloping toward the northwest.  The plateau  seen from a summit having an e l e v a t i o n corresponding to that o f i t s surface and where one o f the major r i v e r trenches does not cut the l i n e o f sight displays an even s k y - l i n e sweeping o f f to the h o r i z o n , and broken only here and there by i s o l a t e d , residuary masses r i s ing above the general l e v e l *  This upland, however,  bears no r e l a t i o n to rock structure, erosion having b e v e l l e d the upturned edges o f the hard rock as w e l l as the s o f t s t r a t a , with the r e s u l t that i t s surface i s e n t i r e l y discordant to the structure o f the highly contorted, metamorphie rocks that outerop over i t so extensively. Along the northern portion o f the Coast range, the general summit-level merges i n t o that o f the Yukon plateau, i n a manner suggesting the synchronous plana(1) tion  o f these two provinces, but during the various  v e r t i c a l movements that have a f f e c t e d these t e r r a n e s , the u p l i f t has been g r e a t e s t along the axis o f the Coast range and l e a s t along that o f the Yukon plateau, which terrane i s thus given the contour o f a huge f l o w ing trough whose median l i n e i s i n a general wa^,marked by the present p o s i t i o n of the Yukon f i v e r from near i t s headwaters in northern B r i t i s h Columbia to Bering ( 1 ) Speneer A.C. B u l l . Geol. Soc. o f America. V o l . XIV. P. 132. Brooks, A.H. "Geography and Geology of Alaska." P r o f . Paper, #45 PP 286-290 U.S.G.S.  (12) Sea* No d i s t i n c t l i n e o f demarcation i n d i c a t e s the boundary between the plateau and mountain p r l v i n c e s ; these, instead, grade i n t o each o t h e r , so that a trans i t i o n b e l t occurs, g e n e r a l l y from 1 to 4 miles wide, in which many o f the points cannot d e f i n i t e l y be said (1) to belong to e i t h e r terrane* The plateau topography i s characterized by two s t r i k i n g f e a t u r e s , the numerous,  irregularly-distributed  wide, deep, steep-walled v a l l e y s , and the e l e v a t e d and i n places s l i g h t l y , u n d u l a t i n g , i n t e r v a l l e y , upland areas.  Over considerable p o r t i o n s , the plateau surface  has been almost i f not quite destroyed by l a t e r erosion, and i n such places the topography consists of  irregular-  l y - d i s t r i b u t e d , rounded h i l l s , many of them g e n t l y contoured and with summits that are i n many cases remark ably uniform i n e l e v a t i o n . Towards the south and west the surface o f the Yukon plateau gradually r i s e s and becomes more and more d i s s e c t e d , and the topography consequently assumes an i n c r e a s i n g l y rugged aspect u n t i l the Coast range i s reached. The topography of the Yukon plateau may be d i v i d e d into two groups;- the Uplands and the V a l l e y s . ( 1 ) Cairns D.D. " A t t i n d i s t r i c t , B.C." G.S.C. Mem. #37, 1913. P. 16.  (13) The Uplands. Over l a r g e portions o f the Yukon Plateau r e g i o n , the plateau c h a r a c t e r i s t i c s are s t i l l w e l l preserved, and numerous fragments o f almost f l a t , or gentl y r o l l i n g upland s t i l l remain in s p i t e o f  sub-aerial  e r o s i v e agencies which tend t o destroy the old surface. Over considerable portions o f the plateau r e g i o n ,  little  t r a c e o f the former upland remains and the topography consists o f i s o l a t e d , g e n e r a l l y rounded, h i l l s , many o f the summits o f which r i s e to an e l e v a t i o n o f the plateau s u r f a c e .  I n places erosion has succeeded i n r e -  moving the plateau surface e n t i r e l y , and only low,  ir-  regular h i l l s remain which show no concordance of summit l e v e l . The plateau surface to be observed to the best advantage mast be viewed from interstream p o i n t s ,  sit-  uated some distance back from the edges o f the master v a l l e y s ; from such p o s i t i o n s the even, g e n t l y  rolling  character o f the plateau i s s t r i k i n g l y apparent.  The  surface bears no r e l a t i o n to rock structure, the various rocks underlying the plateau are a l l truncated,  regard-  l e s s o f t h e i r structure, hardness, composition or other qualities. The plateau-surface thus represents a p l a i n o f erosion that has probably been produced mainly by ordinary e r o s i v e agencies rather than by g l a c i a t l o n ,  (14) since i f i t has been produced by g l a c l a t i o n i t s surf a c e would be everywhere strewn with f o r e i g n g l a c i a l materials, which i s , g e n e r a l l y , not the case.  In places  there i s evidence such as the occurrence o f s t r i a e and e r r a t i c s , that i c e has moved over the l o c a l plateau s u r f a c e , but the g r e a t e r part o f the upland i s covered with l o c a l material produced by ordinary e r o s i v e and weathering agencies. This plateau surface thus appears to form part o f a region that during a long period of c r u s t a l  stabil-  i t y was almost completely b a ^ e - l e v e l l e d and was reduced to a condition o f o l d age.  The residual mountains that  now c o n s t i t u t e monadnocks r i s i n g above the plateau level,  represent the only considerable e l e v a t i o n s that  remained to break the monotony o f the former landscape. B a s e - l e v e l l i n g processes, which tended to reduce the e n t i r e plateau region to s e a - l e v e l were i n t e r r u p t e d , bef o r e the reduction o f these remaining h i l l s , by an upl i f t which a f f e c t e d a great p o r t i o n , at l e a s t , o f B r i t i s h Columbia and Yukon. The Yukon plateau province has been studied by a number o f g e o l o g i c a l observers, among whom there i s a consensus o f opinion that i t represents a region which during a long period o f crustal s t a b i l i t y became almost completely b a s e - l e v e l l e d and was reduced to a s t a t e o f o l d age.  Accordingly at one time t h i s region  (is; East have formed a portion o f a p l a i n , the edge o f which was at o r nearly at s e a - l e v e l .  This base-  l e v e l l i n g process was f o l l o w e d by a widespread u p l i f t and the nearly f l a t or g e n t l y undulating lowland became an upland t r a c t .  This u p l i f t rejuvinated the streams  which immediately commenced trenching t h e i r v a l l e y s i n the upland surface and a new physiographic c y c l e was inaugurated.  There i s some d i f f e r e n c e o f opinion as  to the exact date o f t h i s planation and subsequent upl i f t , but the bulk o f the evidence goes t o show that t h i s region was pinnated during e i t h e r the Eocene o r Pre-Pliocene Post-Eocene time, and that the planated t r a c t was u p l i f t e d to nearly i t s present p o s i t i o n during l a t e Miocene, P l i o c e n e , o r nearly P l e i s t o c e n e (1) time. The amount o f u p l i f t i s somewhat i n d e f i n i t e . The Lewes and Yukon r i v e r s have grades much in excess of r i v e r s t r a v e r s i n g a d i s t r i c t i n i t s o l d age. Further i t seems very improbable that the area,  prior  to u p l i f t , was drained by a longer water system than the present c i r c u i t o u s one; in f a c t ,  investigations  have tended to show that the d i s t r i c t was drained i n t o  (2)  the P a c i f i c by a much shorter system.  The v e r t i c a l  extent o f the u p l i f t was probably in the neighbourhood ( 1 ) Cairns D.D. "Wheaton d i s t r i c t , Yukon T e r r i t o r y . " G.S.C. Mem.#31, 1912 PP 83-84 ( 2 ) Brooks A.H. "Geography and geology Of Alaska," P r o f . Paper #45 U.S.G.S. 19Q6 P. 294.  (16) (1) o f 4500 f e e t . Sometime subsequent to the u p l i f t , and the developement o f the present v a l l e y systems, a c l i m a t i c change caused g l a c i e r s to form i n the higher regions, and great tongues of i c e moved from the gathering grounds down the main v a l l e y s of the plateau and the uplands of the plateau surface were only s l i g h t l y a f f e c t e d .  (2)  Cockfield  i s o f the opinion that g l a c i a t i o n as an i c e -  sheet did net e f f e c t the Yukon plateau.  He b e l i e v e s  that the Coast range and the Mackenzie mountains acted as accumulating centres f o r the i c e which eventually descended upon the plateau in tongues f o l l o w i n g the main r i v e r v a l l e y s and to a small extent covering some o f the upland portions of the p l a t e a u - s u r f a c e .  These  ice-tongues deposited morainal material i n the v a l l e y s and on some o f the upland surfaces; and in some eases formed dams i n the streams due to the rapid r e t r e a t o f the i c e , thus also forming l a k e s . I t has bean calculated that when the C o r d i l l e r a n i e e - s h e e t was present i n North America the snow l i n e was lowered 3,000 f e e t .  In Yukon the snow l e v e l i s 7,  500 f e e t and a lowering o f 3,000 f e e t would place the snow l i n e at 4,500 f e a t .  The general l e v e l o f the  plateau i s approximately 5,000 f e e t , thus the snow l i n e ( 1 ) C a i m s D.D. " A t t i n P.23. d i s t r i c t , B.C." G.S.C. Mem.37, 1913 ( 2 ) Cockfield W.B. Personal Communication.  (17) during the time o f the C o r d i l l e r a n i c e - s h e e t would be w e l l below the general l e v e l o f the plateau.  The accept-  ed reason f o r the absence of g l a c i a t i o n i n Yukon i s the lack o f p r e c i p i t a t i o n *  The Yukon plateau i s a dry b e l t ,  which i s r e a d i l y r e a l i z e d by the volume of water i n the drainage systems.  The Yukon r i v e r drainage basin i s as  l a r g e as that o f the S t . Lawrence r i v e r system but the volume o f water i s only one seventh.  Thus i f ,  during  C o r d i l l e r a n iee-sheet time, the moisture laden winds came from the P a c i f i c i n a southwesterly d i r e c t i o n , as b e l i e v e d , the S t . E l l a s range and the Coast range would prove an e f f i c i e n t b a r r i e r to p r e c i p i t a t i o n over the Yukon Plateau r e g i o n . At no time, apparently, did snow gather on the plateau i n s u f f i c i e n t q u a n t i t i e s t o form considerable masses o f i c e , bat f o r the most p a r t , i t seems to have been blown by the winds i n t o the v a l l e y s and depressions.  I t i s b e l i e v e d t h a t , during P l e i s t o c e n e  and Recent times, the plateau s u r f a c e , although only modified s l i g h t l y by moving i c e , has been considerably a f f e c t e d by accumulations o f snow. The e f f e c t s o f neve snow are to eonvert shallow V-shaped v a l l e y s i n t o f l a t U-shaped depressions, to e f f a c e t h e i r drainage l i n e s without m a t e r i a l l y changing t h e i r grades, and i n t h i s manner to produce general smoothness o f s u r f a c e .  Since the snow-drifts have no  (18) s l i d i n g motion, there i s no transportation o f material by them; however, because o f excessive f r o s t a c t i o n , and continued a l t e r n a t i o n s o f f r e e z i n g and thawing, the rocks at the p e r i p h e r i e s o f the quiescent snow, are f i n e l y comminuted and the material i s removed by i n numerable r i l l s to neighbouring depressions*  These  (1)  e f f e c t s o f the work o f quiescent neve, c a l l e d n i v a t i o n , have resulted i n grading, to a considerable e x t e n t , the already g e n t l y r o l l i n g surface o f the plateau region, and account f o r the great amount o f f i n e material that f i l l s a l l the minor depressions in the upland s u r f a c e . The presence o f the snow also helped to preserve the smooth o u t l i n e s of the topography, by p r o t e c t i n g the surfaces from stream a c t i o n . A review o f the above shows that the f o l l o w i n g causes mainly account f o r the contrasting  topographies  o f the Coast range and Yukon p l a t e a u : 1.  The Coast range was u p l i f t e d :aore than the  plateau t r a c t and was consequently subjected to a g r e a t e r degree to e r o s i v e agenciesg and as the mountains o f the Coast range are composed mainly of homogeneous g r a n o - d i o r i t e the forms produced by erosion are noticeably i r r e g u l a r since no bedding planes or l i n e s o f hard and s o f t l a y e r s e x i s t to be emphasized by degradation. t l } Cairns D.D. " A t l i n P.d i s25. t r i c t , B.C." G.S.C. Mem. 3V, 1913  (25) 2.  The rocks o f the Coast range are g e n e r a l l y  harder and mere r e s i s t a n t t o ordinary sub-aerial agenc i e s than are the rocks to the east* and the more nearl y the rocks o f the plateau approach those of the mount a i n s i n physical p r o p e r t i e s the l e s s apparent, and the more gradual I s the change from plateau to mountain provinces. 3.  The Coast range i s s u f f i c i e n t l y hign to  hold g r e a t amounts o f g l a c i a l i c e which i s  still  actively  employed accentuating the f e a t u r e s o f the mountains and g i v i n g them a t y p i c a l f r e t t e d appearance.  I n the ease  o f the Yukon plateau, on the other hand, the i c e , except f o r small masses i n occasional c i r q u e s , has long sinee vanished from the region, and instead o f the f e a t u r e s there continuing t o become more pronounced, they are being rounded and smoothed ever by n i v a t i o n .  Thus once  a d i f f e r e n c e of e l e v a t i o n between these two provinces was e s t a b l i s h e d , t h e i r f e a t u r e s became continually more and more contrasted.  This aptears to account mainly  f o r the s t r i k i n g d i f f e r e n c e i n the physiography o f the terranes, although apparently synchronously planated (1) and u p l i f t e d * The V a l l e y s . A f t e r having considered the g e n t l y undulatory character o f the upland, the observer w i l l be impressed ( 1 ) Cairns D.D.  Op. c i t . P. 25.  by the praaaameed topographic unconformities that present themselves at the contacts o f t h i s surface with the high, s t e e p l y - i n c l i n e d w a l l s o f the various v a l l e y s til that i n t e r s e c t  it*  The l a s t great u p l i f t , probably i n Pliocene time, which a f f e c t e d t h i s d i s t r i c t , g i v e the streams o f the region renewed l i f e and energy, and they immediately began vigorously trenching t h e i r channels i n the u p l i f t e d surface*  Throughout the area deep i n c i s -  ions were r a p i d l y made, which, i n P l e i s t o c e n e time, were invadad by g l a c i e r s from the mountains to the west aàd south.  Although the i c e produced but l i t t l e  effect  upon the upland s u r f a c e , i t had a profound influence upon the v a l l e y s * When a broad i c e - s h e e t covers a d i s t r i c t  it  has the e f f e c t o f moderating the topographic features and ^educing the r e l i e f , by eroding m a t e r i a l from the higher e l e v a t i o n s and depositing i t i n the depression. However, where the i c e occupies only the v a l l e y s , such g r e a t e r end d i f f e r e n t r e s u l t s are ss-en.  Bare the  interstream areas maintain t h e i r even character, una f f e c t e d by the i c e , x h l l e the v a l l e y s are widened and deepened; and the maximum a f f e c t s of g l a c i a t i o n are produced i n areas where tihe topography indicates that T H " C a i r n s D.D. "Wh&aton d i s t r i c t ^ Yukon T e r r i t o r y ^ " " * * G.8.C. Mem. 31, 1912 P. 16.  (21) 1$ has been previously prepared to r e c e i v e the i c e , by having deep v a l l e y s already made, i n which the i c e can moat advantageously o p e r a t e .  The V-shaped v a l l e y s are  then transformed i n t o wide, deep, s t e e p - w a l l e d , U-shaped depressions, and hanging v a l l e y s , cirques, roches moutonnes, and other w e l l known g l a c i a l forms are produced* In addition to being mainly d e s t r u c t i v e , the g l a c i e r s also acted i n a constructive c a p a c i t y , and cont r i b u t e d vast amounts o f morainal and other materials which deeply covered the f l o o r s of the master-depressions.  Since the r e t r e a t of the i c e but l i t t l e  erosion  has occurred, and considerable portions of these v a l l e y s are s t i l l almost as the i c e l e f t them, and the l a r g e r the v a l l e y s the more m a t e r i a l they have r e c e i v e d . The broad, f l a t - b o t t o m e d , steep-walled v a l l e y s are found only i n southern Yukon and i n the v i c i n i t y o f the mountain ranges, which as noted b e f o r e , acted as c o l l e c t i n g regions f o r the l e e .  Northward, wide,  flat,  g e n t l y sloping v a l l e y w a l l s with i n t e r l o c k i n g spurs are more common.  These are the unglaciated v a l l e y s o f the  plateau province.  The g l a c i a t e d v a l l e y s are usually  dotted with numerous lakes and muskegs bat the nong l a c i a t e d v a l l e y s have a complete drainage system. The small streams that t r a v e r s e the apland f l o w over t h i s sarface i n wide, f l a r i n g depressions, with g e n t l e g r a d i e n t s , but on coming to the edge o f t h i s  (32) e l e v a t e d platform they plunge suddenly, by successive f a l l s , through gorge-shaped i n c i s i o n s , t o j o i n the master streams below.  Thus the t r i b u t a r y streams have  hanging v a l l e y s , and the smaller the t r i b u t a r y , the l e s s eroding power o f the stream, e i t h e r of i c e or water, which i t contained, and the more i t s v a l l e y was l e f t hanging abcve that o f the master stream. P e r f e c t l y developed and w e l l preserved crlques occur p l e n t i f u l l y , and e x i s t p r e v a i l i n g l y along the edges o f the m a s t e r - v a l l e y s .  A notable f e a t u r e i n con-  nection with these forms i s that they are i n v a r i a b l y found along the sides o f the l a r g e r v a l l e y s , or at what may be considered the heads o f the almost i n s i g n i f i c a n t sub-tributaries.  The cirques that o r i g i n a l l y  existed  at the heads o f the l a r g e r t r i b u t a r i e s have, i n a l l cases noted, been successful i n gnawing headward to meet others moving in an opposite d i r e c t i o n , and c o l s o r (1) passes have r e s u l t e d . G l a c i a t i o n has generally extended p r a c t i c a l l y to the top of the c i r q u e - w a l l s , but above and back of t h i s only n i v a t i o n has been o p e r a t i v e .  The snowbanks  are always the forerunners of g l a c i e r s , and when they accumulate on favourable h i l l s i d e s the comminuted materi a l produced i s removed, not as i n the case of  drifts  ( 1 ) Cairns D.D. "Wheaton d i s t 31. r i c t ,1912 "Yukon Territory," G.S.C. Mem. P. 20.  (23) on the upland surface to f i l l miner depressions n e a r l y , and so to moderate the topographic r e l i e f , but instead innumerable r i l l s carry the f i n e l y broken material t o Rarggr waterways which d i s t r i b u t e i t widely*  As t h i s  continues, the d r i f t s enlarge t h e i r containing nooks, and nourishing catchment basins f o r g l a c i a l i c e are soon produced, and i n t h i s way many cirques are formed.  The  boundary between the quiescent neve snow and the g l a c i e r is)marked i n cirques by the w e l l known bergschrund, or s e m i c i r c u l a r , i r r e g u l a r crack that occurs approximately conforming to the contour o f the c i r q u e , but standing somaidistance from i t s walls*  gatthes has calculated  that the neve mast be 125 f e e t thick and on a 12 per (1) cent grade b e f o r e motion commences. From the immediately preceding statement  it  would seem, since the general l e v e l o f the v a l l e y f l o o r s i s roughly 1,500 f e e t below the plateau l e v e l , that  all  the v a l l e y s o f the Yukon plateau should have been g l a ciated.  This i s stated i n view o f the f a c t that the  snow o f the uplands was considered as blown i n t o the depressions, t h e r e f o r e the v a l l e y s should have been f i l l ed with roughly 1,500 f e e t o f snow and the v a l l e y w a l l s having a grade o f g r e a t e r than 12 per cent would produce motion*  There appears to be only one reason why t h i s  ( 1 ) Caims D.D. "Wheaton d i s t r i c t , Yukon T e r r i t o r y . * ' 6 . S . C . Mem 31. 1912 P. 20.  (24) neve d i d not form and t h i s i s that there was not s u f f i c i e n t snow, o r there was not 125 f e e t o f more in the valleys.  As explained b e f o r e , the Yukon plateau i s a  dry b e l t between two mountain systems and the absence o f g l a c i a t i o n i n the northern portion o f the plateau shows that t h i s area was, as now, a dry b e l t .  The moun-  t a i n system on the west protected the i n t e r i o r regions from p r e c i p i t a t i o n but formed the gathering ground f o r the v a l l e y g l a c i e r s which sent out t h e i r tongues o f i c e onto the plateau r e g i o n . I t i s the b e l i e f o f the w r i t e r that too much e r o s i v e power i s a t t r i b u t e d to g l a c i a t i o n , i n the lower levels especially.  G l a c i a t i o n , i n the w r i t e r ' s opinion,  i s more o f a moulding, somewhat scourging, process i n w&lch the sharp l i n e s o f n o n - g l a v i a l erosion are e f f a c e d . I t i s probable, t o o , that the e r o s i v e power o f  glacia-  t i o n i n the higher l e v e l s may be due to f r o s t action and the extremes o f temperature.  These conclusions are  engendered by the w r i t e r ' s l i m i t e d experience with g l a c i a t i o n and w i l l be c h e e r f u l l y r e c a l l e d in favour o f evidence to the contrary. In a number o f places i n the v a l l e y s  terraces  are found, which are o f t e n quite p e r s i s t e n t and e x i s t up to 700 or 800 f e e t above the v a l l e y bottoms.  These  are p e c u l i a r i n t h a t , although from a distance,  prefer-  ably from the other side o f the v a l l e y in which they  (35) occur, they may be quite evident and even somewhat s t r i k i n g on account o f t h e i r p e r s i s t e n c y , s t i l l when a person i s a c t u a l l y on the spot where they occur? i s o f t e n d i f f i c u l t to t e l l e x a c t l y where they  it  lie,  since o n l y s l i g h t amounts o f t e r r a c e - t o p s o r platforms  (1)  remain.  Generally s e v e r a l o f these t e r r a c e s can be seen c l i n g i n g to the v a l l e y - w a l l s , and i n a few places f o u r o f f i v e may e x i s t , one above the o t h e r . the m a j o r i t y extend but a short d i s t a n c e .  Of these,  These t e r r a (2)  ces have been described by a number o f w r i t e r s ;  and  everywhere the o r i g i n o f these t e r r a c e s i s i n doubt. Dawson and Spurr consider that subsequent to the u p l i f t o f the Yukon plateau, and a f t e r the v a l l e y s had become deeply trenched, a submergence occurred i n l a t e o r Pleistocenetime.  The v a l l e y s are thus thought to  have become p a r t l y f i l l e d with g r a v e l s , sands, etc*  Pliocene  silts  A f t e r a b r i e f p e r i o d , e l e v a t i o n commenced, and  as the streams cat down through the d e b r i s t e r r a c e s were l e f t c l i n g i n g t o the v a l l e y w a l l s - - the amounts ( i ? Cairns D.D. "Wheaton d i s t r i c t , Yukon T e r r i t o r y , " G.S.C. Mam 31. 1912 p. 21 ( 2 ) Dawson G.M. "Trans. Roy. Soc. Can. Vol V I I I , Sec 4, 1890, PP. 36-41, 48, 49. McConnell R.G."An.Rep.Geol.Snrv. Can. Vol.IV,1888-89. Russell j . c . " B u l l . G e o l . S e c , o f Amer. V o l . 1 , P . 1 3 9 . Spurr J.B* "Geology o f the Yukon Gold d i s t r i c t , " 18th An.Rep. U.S.G.S. P t . I l l , 1 8 9 6 - 9 7 PP. 268-69. Sordenskjold O.The American Geol. Vol.XXIII.PP.290-98 Brooks A.H. "Prof.Paper #45,1906,9.S.G.S. P.296.  (26) o f the subsidence and u p l i f t being indicated by the terraces* The postulation o f a submergence and subsequent (1) u p l i f t appears to Caimes  to be quite uncalled f o r , to  explain the o r i g i n o f these t e r r a c e s .  Quoting C a i m e s ; -  "Tt i s true that a c e r t a i n amount o f u p l i f t has occurri ed i n recent times and may be s t i l l i n progress, as i n dicated by recent rock t e r r a c e s along the Yukon r i v e r above Dawson and elsewhere, but these appear to have had an o r i g i n q u i t e d i s t i n c t from the g r a v e l , sand and s i l t t e r r a c e s which characterize many o f the v a l l e y s o f northern B r i t i s h Columbia and Yukon.  In whatever manner  the terraces were formed, they must have o r i g i n a t e d since the g l a c i a l p e r i o d , otherwise the v a l l e y g l a c i e r s would have e n t i r e l y o b l i t e r a t e d them.  I t i s f u r t h e r evident  that no great amounts o f m a t e r i a l have been deposited i n many o f the v a l l e y s since g l a c i a l time, as i n depressions such as along the White Pass and Yukon railway between Corcross and Whitehorse, and around Annie l a k e , the v a l l e y f l o o r i s pot-holed and minutely rough, and possesses s t i l l the c h a r a c t e r i s t i c appearance o f a surf a c e that has been o v e r l a i n by i c e . " Brocks and others have supposed the t e r r a c e s to be due to changes i n the e r o s i v e powers o f the stream, and i n places t h i s appears to be t r u e , but i n the peri l ) C a i m e s D.D.  Op. c i t .  P.22.  (27) t i o n o f Yukon t e r r i t o r y where the terraces reach high up on the v a l l e y w a l l s , t h i s theory c a l l s f o r the f o r mer existence o f v a s t amounts o f material over the present v a l l e y f l o o r s , which cannot be true in some l o c a l ities* I t has been supposed that the t e r r a c e s are remnants o f l a t e r a l moraines formed along the edges o f the v a l l e y g l a c i e r s , and consist thus p a r t l y o f groundup debris accumulated by the i c e i t s e l f , and p a r t l y o f materials that r o l l e d down the s i d a h i l l s from above, and gathered along the Upper surface o f the i c e .  As  the i c e r e t r e a t e d , and stood at successively lower e l e v a t i o n s , ether accumulations would tend to form, and those l e f t above would remain i n the form o f c l i n g i n g to the v a l l e y walls*  terraces  The most p e r s i s t e n t and  prominent o f the t e r r a c e s would thus mark e l e v a t i o n s at which the i c e maintained constant e l e v a t i o n s f o r excepti o n a l l y long p e r i o d s . I n c e r t a i n v a l l e y s where the terraces have been but poorly preserved i t i s d i f f i c u l t to disprove t h i s theory.  However, i n some cases, quite extensive  flat-  topped t e r r a e e accumulations remain i n the meuths o f the t r i b u t a r i e s , and extend out f l u s h with the edge o f t h e ^ a l l s o f the m a s t e r - v a l l e y .  I f the terraces o r i g i n -  ated due to l e e a c t i o n , the i c e would also have invaded the mouths o f the t r i b u t a r i e s , and the e n t i r e lower  (28) portions o f such would not now contain f l a t - t o p p e d accumulations. I t thus seems e v i d e n t , as suggested by Nordens k j o l d and o t h e r , that these t e r r a c e s are dominately, at l e a s t , lake t e r r a c e s , and represent successive e l e v a t i o n s at which the water stood i n p o s t - g l a c i a l  time.  This c a l l s f o r a damming o f the drainage system somewhere along the Yukon r i v e r .  As the terraces i n d i c a t e  that the period o f submergence was only b r i e f , the damming was probably due to accumulations o f i c e o r other g l a c i a l m a t e r i a l s . The g r e a t masses o f i c e which occupied the master-depressions planated the v a l l e y s i d e s , reducing a l l p r o j e c t i n g spurs, r i d g e s , e t c , and bringing them i n t o alignment to form quite regular w a l l s .  Since the  close o f the g l a e i a l epoch, the numerous small t r i b u t a r y streams from the upland have been cutting channels i n these w a l l s and enlarging the p r e - g l a c i a l I n c i s i o n s i n them.  The r e s u l t i s t h a t , cat i n these  steeply-inclin-  ed v a l l e y slopes are numerous V-shaped, t r e n c h - l i k e fOrms, and between these are f a c e t t e d forms carved i n the v a l l e y - w a l l s .  These forms are quite pronounced  along the g l a c i a t e d v a l l e y s and represent forms produced by a combination o f g l a c i a l and p o s t - g l a c i a l  activit-  ies. The stractual c o n t r o l o f drainage courses and  (89) A the e f f e e t o f rook structure upon topography i n Yukon are questions which have not been d e a l t with at length by g e o l o g i s t s and ethers w r i t i n g o f the r e g i o n .  (1) Cairnes  s t a t e s that the present course o f Yukon r i v e r marks the axis o f the Yukon plateau^ towards which there i s a gradual slope both from the e a s t , and that t h i s was (2) caused by d i f f e r e n t i a l u p l i f t .  C o c k f i e l d and B e l l are  o f the opinion that a number o f the l a r g e r v a l l e y s i n Whitehorse d i s t r i c t l i k e w i s e had t h e i r p o s i t i o n d e t e r mined to a g r e a t extent by structural f a c t o r s .  They  also noted a rather s t r i k i n g rectangular e f f e c t i n the drainage o f the McClintock basin, which suggest struct u r a l control o f ( 3drainage* ) Reinecke  noted the r e l a t i o n of drainage to  structure i n the I n t e r i o r plateau o f B r i t i s h Columbia* There, he found the general trend o f the drainage to be north, northwest and northeast and also noted a marked r e c t i l i n e a r i t y i n drainage p a t t e r n .  Reinecke i s o f the  opinion that the drainage i s c o n t r o l l e d by f r a c t u (r4e )s trending north northwest and northeast.  Schofleld  finds  that the f r a c t u r e system o f B r i t i s h Columbia has three main d i r e c t i o n s north, northwest and northeast. ( 1 ) C a i m e s D.D. "wEeaton d i s t r i c t , Yukon T e r r i t o r y . " G.S.C. Mem 31 PP. 84. 1912. ( 2 ) C o c k f i e l d W.E. & B e l l A.H. "Whitehorse d i s t r i c t , Yukon." G.S.C. Mem. 150 P.5. 1926. ( 3 ) Reinecke L . "Physiography of the Beaverdell-Map Area and the Southern Interior."G.,S.C. Mus. 1915. ( 4 ) S c h o f i e l d S.J.B u l l . 11G.I.M.M. - - Bull.  (30) Although thero I s l i t t l e information on the f r a c t u r e system o f the Yukon t e r r i t o r y , from a study o f the drainage pattern there appears to be a d e f i n i t e design.  Most o f the streams have a general north, north-  west or northeast trend and some r e c t l l i n e a r i t y i s noted. I t thus seems probable and p o s s i b l e that the f r a c t u r e system o f B r i t i s h Columbia may be extended i n t o Yukon. As has been shewn, g l a e i a t i c n has modified the v a l l e y s o f the streams and has l e f t deposits o f moraina l material upon the v a l l e y f l o o r s ; but g l a e i a t i o n has also modified the drainage*  On the wide, f l a t v a l l e y -  bottoms o f the g l a c i a t e d v a l l e y s innumerable pot-hole lakes are found.  These lakes are due p a r t l y to the  scouring action o f the i c e bat mainly to the disruption of the o r i g i n a l drainage by damming with g l a c i a l d e b r i s , l e a v i n g a disconnected drainage system. Through the g l a c i a l debris the r i v e r s wend a rather sinuoas course and some lakes are formed by the cutting o f f o f ox-bows.  In quite a number o f eases, the  drainage has been reverted by the damming o f the ancient v a l l e y With morainal material and, as i n the ease of Miles canyon near Whitehorse, with recent f l o w s . An inspection o f the map suggests certain rather obvious changes that may have taken p l a c e .  Lewes r i v e r  may have flowed through the lower part o f the v a l l e y o f Watson r i v e r Instead o f around by lake Bennett.  Wheaton  r i v e r may have f o l l o w e d i t s same course above Big Bend and here turned to the l e f t instead of to the r i g h t , f l o w i n g northward through the v a l l e y now occupied by (1) f Annie l a k e .  C o c k f i e l d and B e l l  are o f the opinion  that changes such as these were due perhaps, to one or both o f two f a c t o r s : 1. d e p o s i t i o n o f g l a c i a l materials i n the former v a l l e y s and 2. diastrophic movements.  (2)  Caimes  suggests that the Lewes r i v e r formerly flowed  through the O g i l v i e v a l l e y , which i s a continuation o f that occupied by lake Laberge, and which channel has been f i l l e d with morainic and other d r i f t m a t e r i a l during the g l a c i a l p e r i o d , f o r c i n g the r i v e r to seek i t s present course.  (3)  The evidence i n Upper White River d i s t r i c t would seem to i n d i c a t e that Upper White r i v e r i n p r e G l a c i a l time f o l l o w e d a course s i m i l a r to that of ^he present stream as f a r as the I n t e r n a t i o n a l Boundary, but below that p o i n t , t h i s r i v e r swung to the north and continued down through Lake Tchawsahonon v a l l e y to the Beaver.  The Genere r i v e r , on the other hand,  apparently held p r a c t i c a l l y i t s present course to the White River v a l l e y , and thence p e r s i s t e d as now, through the Nutzotin mountains, was joined by Koldem r i v e r and  ( 1 ) Cockfield W.R. and h e l l , A.R. "Whitehorse d i s t r i c t , ( 2 ) Caimes D.D. ( 3 ) Caimes D.D.  Yukon.* G.S.C. Hem 150 P.5 1926. "Lewes and Nordenskiold r i v e r s , Yukon." G.S.C. Mem.5 P.15 1910. "Upper White River d i s t r i c t , Yukon." G.S.C. Mem. 50 P.61 1915.  (38) other streams and was united with the Upper White r i v e r which had been j o i n e d by the waters of the Upper Tanana. These combined streams then may have flowed e i t h e r down the Tanana and thence to the Yukon, o r may have continued down the present v a l l e y of the White to the Donjek r i v e r a decided change occurs.  The v a l l e y o f the White  above t h i s point i s wide and contains on e i t h e r side heavy banks and t e r r a c e s o f g l a c i o - f l u v i a l accumulations. Below the Donjek these are suddenly replaced by high abrupt rock c l i f f s * and the v a l l e y instead o f having an o l d appearance, e x h i b i t s considerable evidence o f being a youthful depression.  Thus i n a l l p r o b a b i l i t y a form-  er r i v e r drained through the present v a l l e y o f the White to the mouth o f the Donjek, but thence f o l l o w e d some other route to the p r e - G l a c i a l channel of theYukon r i v e r . The Upper White, according to t h i s system o f drainage, came very close to the Generc and, due possibly to g l a c i a l accumulations, was eventually turned i n t o  it  over the present p o s i t i o n o f the Upper canyon. (1) Cockfield  i s o f the opinion that from where  the P e l l y r i v e r swings sharply to the south to j o i n the Yukon r i v e r i t has l e f t i t s o l d v a l l e y .  This ancient  v a l l e y i s approximately ten miles wide and extends to j o i n the Stewart r i v e r .  There i s a d i f f e r e n c e o f e l e v a -  t i o n i n the ancient v a l l e y o f about 300 f e e t , t l ) C o c k f i e l d W.E.  Personal Communication 1930.  (33) He also stated that the Yukon r i v e r enters a t o t a l l y d i f f e r e n t v a l l e y north o f i t s junction with the P e l l y r i v e r *  Sooth o f t h i s junction the Yukon  r i v e r f l o w s i n a wide, f l a t v a l l e y with rounded h i l l s while north o f t h i s junction i t f l o w s i n a narrow steepwalled v a l l e y .  He a t t r i b u t e s these changes to accumu-  l a t i o n o f g l a c i a l debris* Farther d e t a i l e d i n v e s t i g a t i o n w i l l be necessary b e f o r e the drainage changes w i l l be understood, and the former drainage system i s established*  (54) GENERAL  GEOLOGY*  & great v a r i e t y o f rocks, both sedimentary and igneous and ranging i n age from Pre-Cambrian to Secant, are found throughout the Yukon t e r r i t o r y . The o l d e s t rocks are metamorphic and are domin(1) antly schistose i n character.  They are considered  be, mainly, o f sedimentary o r i g i n .  to  These metamorphic  schistose rocks consist dominantly o f schistose amphib o l i t e s , q u a r t z l t e s c h i s t s , mica schists,, and occasiona l beds o f limestone and are known as the Yukon group. Occasional dykes and small i n t r u s i v e bodies pierce the Palaeozoic beds i n places, and greenstones of various types have a considerable developement in association with c e r t a i n o f the Lower Cambrian or Pre-Cambrian members, and occur as s i l l s , dykes or l a r g e r i r r e g u l a r i n t r u s i v e masses.  The evidence obtained regarding  these rocks, i n d i c a t e s rather conclusively that they are a l l o f Pre-Cambrian age. Overlying the metamorphic schistose rocks i s a group o f rocks composed mainly of dolomites, quartz l t e s shales, s l a t e s , p h y l l l t e s , and associated greenstones.  These are known as the T i n d i r group and are  considered as younger than the Yukon group o f PreCambrian age. ( 1 ) Cairnes D.D. "The Yukon-Alaska I n t e r n a t i o n a l boundary between Porcupine and Yukon r i v e r s . " G.S.C. Mem 67 P. 35 1914.  (35) The T i n d i r group i s o v e r l a i n , unconformably, by a thick s e r i e s o f limestone-dolomite beds which range i n age from Cambrian t o Carboniferous.  Shales,  c h e r t s , sandstones, cherty conglomerates and t h i n l y bedded limestones are found ranging i n age from Ordov i c i a n to Carboniferous.  These beds are i n turn over-  l a i n by a thick s e r i e s of sediments composed domlnantl y o f shales, sandstones and conglomerates with occasi o n a l i n t e r c a l a t e d beds o f limestones that are of Pennsylvanian or Permian age.  These compose the Nation  River formation. Apparently conformably, o v e r l y i n g the Nation River formation i s a thick s e r i e s o f Hesozoic sediments including mainly shales, sandstones, greywackes, conglomerates, s l a t e s and q u a r t z i t e s .  F o s s i l s have been  found i n these rocks i n d i c a t i n g a Cretaceous age. I n v e s t i g a t i o n s , so f a r , have f a i l e d to show any l a r g e basins o f T e r t i a r y sedimentation as occur in the I n t e r i o r plateau region o f B r i t i s h Columbia.  A  few small basins o f sedimentary T e r t i a r y are known to occur i n the c e n t r a l portion of the Yukon plateau.  More  recent than these consolidated roek formations are the s u p e r f i c i a l deposits o f s i l t s and g l a c i a l debris of Recent and P l e i s t o c e n e times.  These Recent and P l e i s t o -  cene deposits form a mantle obscuring the o l d e r format i o n s throughout a l a r g e portion o f Yukon.  (36) The igneous roeks throughout the region consist o f i n t r u s i v e and e x t r u s i v e phases.  The i n t r u s i v e rocks  are represented by the Coast Range i n t r u s i v e s , which consist mainly o f g r a n o - d i o r i t i c roeks.  They form the  Coast Range b a t h o l i t h and occur as outlying stocks i n the plateau r e g i o n .  These rocks are considered o f  Jurassic o r younger i n age. Older than the Coast Range i n t r u s i v e s i s a s e r i e s o f igneous rocks composed o f d i o r i t e s ,  andesites,  a n d e s i t l c t u f f s , pyroxenites, amphibolites, and magnesites.  Cf t h e i r age nothing i s known except that they  are o l d e r than the Coast Range. The e x t r u s i v e phase o f the igneous rocks i s represented by a s e r i e s o f f l o w s , t u f f s and b r e c c i a . Younger than the Coast Range i n t r u s i v e s i s a wide-spread s e r i e s o f andesites and andesitic t u f f s and b r e c c i a s . Some o f these are considered contemporaneous with and some younger than the Jura-Cretaceous sediments.  More  recent than these a n d e s i t i c flows are l a t e T e r t i a r y or P l e i s t o c e n e b a s a l t s occurring mainly i n the ibrm o f flows*  These l a t e r flows were, i n p l a c e s , accompanied  by extensive accumulations o f basalt t u f f s .  About t h i s  time a number o f dykes and small stocks o f g r a n i t e and syenite-porphyry were also intruded, but i t i s not known whether b e f o r e or a f t e r the b a s a l t s .  The most recently  (37)  consolidated recks consist of a series of  rbyolites,  trachytes, and l a t i t e s , which pierced the older rocks and poured over the country in places, generally in sheets 50 f e e t or less in thickness.  These outpourings  were accompanied by great quantities of t u f f s and breccias.  Scanned by UBC Library  The o l d e s t pocks known to occur i n Yukon are the Yukon group, and consist mainly o f mica s c h i s t s , quartz-mica s c h i s t s , and schistose amphlbolites, which are considered to be o f Pre-Cambrian age*  These rocks  are so highly metamorphosed that they a f f o r d very  little  information concerning t h i s e a r l y period i n the g e o l o g i c a l h i s t o r y o f the area.  They show that great t h i c k -  ness o f arenaceous and a r g i l l a c e o u s sedinents were deposited i n a probable Pre-Cambrian sea which occupied t h i s region at t h i s time.  They also show that these  sediments have been invaded by various igneous rocks, and that a l l have since become so metamorphosed as to be dominantly schistose o r gneissoid i n character. The Yukon group probably represents the northward extension o f the Pre-Cambrian rocks o f  central  B r i t i s h Columbia and with the T i n d i r group o f  relatively  unaltered sedinents may possibly represent a continuat i o n o f the Pre-Cambrian sea-way from southern B r i t i s h (1) Columbia to the A r c t i c ocean as suggested by S c h o f i e l d . The T i n d i r formation may also comply with S c h o f i e l d ' s B e l t i a n o f the Cranbrook region o f B r i t i s h Columbia. During Lower Palaeozoic times great thickness( g j Schofield S.J.  Trans. Roy. Soc. o f Can. X V I I I . P t . A. 1925.  (39) es o f a r g i l l a c e o u s and arenaceous matter, f o l l o w e d by calcareous m a t e r i a l s , were deposited i n a sea-way. Vulcanism was also a c t i v e .  The Lower Palaeozoic term-  inated i n Yukon with a wide-spread, dynamic revolution which caused extensive deformation and metamorphism, and was accompanied by considerable v o l c a n i c  activity.  I t i s probable that some o f the i n t r u s i v o s may have been I n j e c t e d at t h i s time. Where the records are s t i l l l e g i b l e , they show that at the close o f the S i l u r i a n disturbance a considerable area was above the sea and a long erosion i n t e r v a l ensued.  Some time b e f o r e the Middle Devonian a great  part o f Yukon sank beneath the sea, and at about that time vulcanism became a c t i v e at a number o f p o i n t s . This sea-invasion, which commenced in Devonian time, continued w e l l into the Carboniferous p e r i o d . normal course o f sedimentation was, however,  The  repeatedly  interrupted by v o l c a n i c a c t i v i t y , as a r e s u l t o f which a n d e s i t l c and b a s a l t i c lavas were extruded.  I t seems  probable that c e r t a i n members of these volcanics may be (1)  contemporaneous with the Carboniferous  sediments.  Marine occupation with i t s accompanying sedimentation continued from Carboniferous u n t i l w e l l i n t o Cretaceous time, and during the Mesozoic epoch, arena( 1 ) Cairnes D.D* "Upper White River d i s t r i c t , Yukon," G.S.C. Mem 50 P.112 1915.  (40) ceous and a r g i l l a c e o u s sediments were deposited which have now become a l t e r e d i n t o shales, a r g i l l i t e s ,  sand-  stone, greywackes, and conglomerates* Throughout the western portions o f B r i t i s h Columbia and southern Yukon, a widespread c r a s t a l movement occurred i n Jurassic times and possibly  earlier,to  l a t e r , which was accompanied by the i n t r u s i o n of vast amounts o f igneous materials including a g r e a t p a r t , at l e a s t , o f the roeks composing the Coast Range b a t h o l i t h . At the c l o s e o f the Jurassic disturbance a considerable area was above the sea, and what was probably a short period o f erosion ensued* Cretaceous roeks are known t o contain pebbles o f g r a n i t i c rocks, which are s i m i l a r , l i t h e l o g i c a l l y ,  to  the Coast Range I n t r u a i v e s , and t o be eat by l i t h o l o g i e a l l y s i m i l a r g r a n i t i c rocks.  I t i s evident,  therefore,  that g r a n i t i c intrusions apparently derived from the same magma, have invaded t h i s same general b e l t at d i f f erent and, i n some p l a c e s , widely separated periods ranging from sometime i n , o r previous t o , the Jurassic u n t i l at l e a s t the c l o s e o f the Cretaceous. The Mesozoic e r a , and p a r t i c u l a r l y the l a t t e r part o f i t , was also characterized by v o l c a n i c  activity  as a r e s u l t o f which the Mesozoic and Carboniferous sediments became i n t e n s i v e l y invaded by andesites, d i a bases, b a s a l t s , and r e l a t e d roeks.  As mentioned pre-  (41) v i o u s l y these rocks were considered t o be interbedded with the Carboniferous sediments, and i t was thus conHi sidered p o s s i b l e that these e l d e r v o l c a n i c s represent a long i n t e r m i t t e n t period o f vulcanism extending from  (2)  Carboniferous u n t i l l a t e Cretaceous times.  Coekfield,  however, I s o f the opinion that these Carboniferous rocks belong high up i n the Mesozoic e r a . The Mesozoic period o f sedimentation was termi n a t e d , at or about the c l o s e o f Cretaceous time;by a widespread deformation, at the c l o s e o f which a considerable portion of Yukon was above the sea.  Degradation  became a c t i v e , and no evidence has, so f a r , been obtained to show that from then to present time, any portion o f t h i s region has been subjected to marine c o n d i t i o n s . During e a r l y T e r t i a r y time fresh-water sediments were deposited throughout considerable portions o f Yukon.  The beds were f o r the g r e a t e r part at l e a s t ,  deposited i n shallow basins and i n places contain seams of l i g n i t e .  Previous t o the d e p o s i t i o n o f the e a r l y  T e r t i a r y beds, and a f t e r the deposition o f the Cretaceous sediments, an extensive and far-reaching period o f deforma t i o n ensued corresponding apparently to the Larrimide r e v o l u t i o n elsewhere. ( l ) C a i m e s D. D. "Uuper White River d i s t r i c t Yukon." *" G.S.C. Mem 50* P. 114 1915. ( g ) C o c k f l e l d W.B* Personal Communication. 1930.  (42) A f t e r the deposition o f the T e r t i a r y beds, a gradual u p l i f t occurred which though of orographic character, was i n places accompanied by v o l c a n i c  activ-  i t y and by a considerable disturbance o f the Eocene sediments.  This movement a f f e c t e d apparently a l l of the  Yukon plateau as w e l l as the Coast range. (1) Much discussion has ensued about the actual time o f t h i s period o f crustal s t a b i l i t y but i t would (2) seem from evidence given by Caimes  that the planation  o f the Plateau region was contemporaneous with the dep o s i t i o n o f the Eocene beds.  Some discussion has ensued  both f o r and against the synchronous planation o f the Yukon plateau and the Coast range by the above w r i t e r s .  (2)  Caimes  i s o f the opinion that they were synchronously  eroded but b e l i e v e s that considerable r e l i e f remained. (2) Caimes b e l i e v e s the Coast range and the Yukon plateau were synchronously u p l i f t e d but that the Coast HI) Brooks A.H. "The geography and geology o f Alaska,^ U.S.G.S. Prof.Paper #45 PP 292,293 1906. Spencer A . C . " p a c i f i c Mountain systems i n B r i t i s h Columbia and Alaska;" Bull.Geol.Soc.Amer. V o l . 14 1903. PP. 117-132. Dawson G.M+ "On the l a t e r physiographlcal geology of the Rocky Mountain region i n Canada, with s p e c i a l r e f e r e n c e s to changes i n e l e v a t i o n and the h i s t o r y o f the g l a c i a l period. Trans.Roy.Soc.Can.Yol.111 Sec IV 1890 PP. 11-17. Spurs J.E. "Geology o f the Yukon Gold d i s t r i c t , A l a s k a . " U.S.G.S. 18th An.Rp. P t . I I I . . 1898 PP 260,262,263. ( 2 ) Caimes D.D."Upper White River d i s t r i c t , Yukon," G.S.C. Mem 50.PP. 115-118 1915  (43) range being near the edge was u p l i f t e d more than the Central t r a c t which was near the axes. The T e r t i a r y p e r i o d , p a r t i c u l a r l y a f t e r Eocene time, was also one o f p e r s i s t e n t v o l c a n i c a c t i v i t y .  It  i s probable that these f l a t - l y i n g lavas were poured over (1) the surface from vents and are considered to have flowed out over a region o f considerable topographic d i v e r s i t y . These f l o w s are l a t e r than the d i s s e c t i o n that (2) followed the u p l i f t of the plains and are indeed Recent. L a t e r than the above lavas and i n p r e - G l a c i a l time v o l e a n i c a c t i v i t y was present in Yukon.  These  v o l e a n l c s occur both as i n t r u s i v e s and extrusives and apparently a l l o r i g i n a t e d from l o c a l v e n t s .  ( 1 ) Caimes D+D.*Upper White River d i s t r i c t , Yukon." G.S.C. Mem. 50 P.118 1915. ( 2 ) Mendenhall W.C. "Geology o f Central River region A l a s k a . " U.S.G.S. Prof paper #41, 1905, P. 57.  o— - 4 F  -O  ^ ^ t ^ ^  5  § 53 ^  ^ ^ ^  S  -o  A  !  h ^  s í  M  i !  s  ^ S  --o  ? N t ^  -  -t  -oo  j $ x:  o  ^^^  Si  .Ss  ^ ^ ìi  ì  st  S!  {  S  (44) PRE-CAMBRIAN  ROCKS.  The Pre-^ambrian rocks o f the Yukon region are grouped, i n t h i s t h e s i s , under the term Yukon group. They are exposed over a l a r g e area of the Plateau region and are considered to be p o s s i b l y underlying the whole o f the Yukon plateau. The rocks o f t h i s group are dominantly  schis-  tose i n structure and consist mainly o f q u a r t z i t e schist schistose amphibolites c h l o r i t e s c h i s t ,  granite-gneiss,  and mica schists but a l s o Include thin bands o f l i n e limestone*  crystal-  A l l these members are much f o l d e d ,  f a u l t e d and d i s t o r t e d , and are so metamorphosed that i n places i t i s d i f f i c u l t to or impossible to determine (1) t h e i r o r i g i n or o r i g i n a l  characters*  The q u a r t z i t e - s c h i s t s are  characteristically  l i g h t t o dark green, f i n e l y textured rocks which have a decidedly schistose structure, but which cleave imperf e c t l y along the planes o f s c h l s t o s i t y , and break prev a i l i n g l y i n t o rough, somewhat p l a t y o r o c c a s i o n a l l y i n t o prismatic fragments, due to more than one s e t o f cleavage surfaces being developed. -Under the microscope these rocks are seen to consist dominantly o f intergrown ( 1 ) Cairnes D.D. "Yukon-Alaska I n t e r n a t i o n a l Boundary between Porcupine and Yukon r i v e r s . " G.S.C. Mem 67. P. 38 1914.  (52) and i n t e r f i n g e r e d quartz grains associated with which are varying amounts o f c h l o r i t e , c a l c i t e and i r o n o r e . G e n e t i c a l l y these rocks are sheared and metamorphosed q u a r t z i t e a and r e l a t e d sediments. The amphibolites are c h a r a c t e r i s t i c a l l y  finely-  t e x t u r e d , dark green rocks with a marked schistose s t r u c t u r e , which c l e a v e only i m p e r f e c t l y , however, along the planes o f s c h i s t o s i t y and break as a rule i n t o rough, i r r e g u l a r , o f t e n somewhat prism shaped fragments.  When  examined under the microscope these roeks are found to be composed mainly o f green hornblende, d l o p s i d e , and carbonates, but contain, a l s o , varying amounts of f e l d s p a r , s e r l c l t e , sphene, and i r o n ore*  quartz,  These amphi-  b o l i t e s are e v i d e n t l y impure sandstones, greywackes,or arkoses, that have become much a l t e r e d . The mica s c h i s t s are g r e y , medium-grained, and with a pronounced developement o f mica on the planes o f schistosity.  They consist o f quartz and mica, with  subordinate f e l d s p a r and c h l o r i t e *  The proportion o f  quartz to mica v a r i e s widely i n d i f f e r e n t specimens; ranging from types i n which mica i s abundantly developed to others i n which the mica i s rather sparse, and which approach q u a r t z i t e s i n composition. are usually intergrown.  The quartz-grains  The mica i s i n p a r a l l e l bands  that o c c a s i o n a l l y show intense p l i c a t i o n , even i n a band specimen, sweeping i n a s e r i e s o f curves through  (46) the specimen. The c l o r i t e s c h i s t s are b r i g h t green t o grey rocks with pronounced f o l i a t i o n , and a g l i s t e n i n g appearance on a f r e s h l y broken s u r f a c e .  They consist o f vary-  ing amounts o f c h l o r i t e , b i o t i t e , and hornblende, with l a t h s o f f e l d s p a r , and minor amounts of magnetite. The g r a n i t e - g n e i s s i s grey to pink, with chara c t e r i s t i c g n e i s s o i d t e x t u r e , ;nd i n some l o c a l i t i e s with an abundant developement o f c r y s t a l s o f f e l d s p a r forming an augen g n e i s s .  I t consists e s s e n t i a l l y o f  quartz, o r t h o c l a s e , p l a g i o c l a s e , b i o t i t e o r hornblende o r both, and micropegmatite.  The quartz and f e l d s p a r  In some cases show granulation, but i n most cases the quartz grains are intergrown, with a satured t e x t u r e . Mica when present i s arranged i n p a r a l l e l bands.  In  some specimens the i n d i v i d u a l leaves o f mica show bending o r crushing against an i n d i v i d u a l o f quartz or f e l d spar. The limestones vary from white to brown, and are more o r l e s s impure, being usually quite  siliceous.  P r a c t i c a l l y a l l t r a c e s o f the o r i g i n ; 1 bedding has been obscured.  These c r y s t a l l i n e limestones appear i n places  to represent I n f o l d e d portions o f more recent beds but i n other p l a c e s , however, the limestone i s  intercalated  somewhat r e g u l a r l y , and has every appearance of being,  (47) and probably i s contemporaneous with the schistose  (1)  members.  The age and c o r r e l a t i o n o f these metamorphic schistose rocks had a f f o r d e d g e o l o g i s t s , working i n  (2)  Yukon, a g r e a t deal o f t r o u b l e .  Cairnes  has t h e i r horizon d e f i n i t e l y determined.  apparently He found Pro-  Middle Cambrian sediments to be o v e r l y i n g the schistose rocks.  The next d i f f i c u l t y i s the c o r r e l a t i o n o f pro-  bably s i m i l a r rocks o f other areas with t h i s known area. The other exposures o f metamorphic rocks are c o r r e l a t e d by l i t h o l o g y which i s a rather uncertain method.  In  many places there s t i l l remains a g r e a t amount of unc e r t a i n l t y regarding t h e i r age and o r i g i n .  Still  It  seems f a i r l y c e r t a i n that there does e x i s t a Pre-Cambrian ( ? ) metamorphic complex underlying a l l ( 3the sed) imentary rocks o f known age throughout Yukon.  ( 1 ) Cairnes D.D. "Yukon-Alaska I n t e r n a t i o n a l Boundary between Porcupine and Yukon r i v e r s . " G.S.C. Mem.67. P.39 1914. PP. 40-44. (2) Idem ( 3 ) Cairnes D.D. "Yukon-Alaska boundary between Porcupine and Yukon r i v e r s . " G.S.C. Mem 67.P.44.  (48) PALAEOZOIC  ROCKS.  CAMBRIAN Pre-Middle Cambrian. (1) Books o f t h i s age have been described  as being  composed dominantly o f sedimentary rocks, but includes a l s o , i n most places, some basic v o l c a n i c s which are In a g e n e r a l way designated as greenstones. t a r y rocks include, mainly, q u a r t z i t e s ,  The sedimendolomites,  s h a l e s , s l a t e s p h y l l i t e s , and also occasional beds o f conglomerate and magnesite.  In d i f f e r e n t  localities  the formation v a r i e s g r e a t l y i n i t s general  lithological  aspect due to the predominance of c e r t a i n members. These rocks are a l l grouped together as PreMiddle Cambrian i n age, however, since these beds are u n f o s s i l l f e r o u s the grouping and c o r r e l a t i o n depends upon l i t h o l o g i c a l c h a r a c t e r i s t i c s , which are by no means infallible. These Pre-Middle Cambrian rocks have been described from only one l o c a l i t y , namely, along the 141st. meridian between Porcupine and Yukon r i v e r s . The q u a r t z i t e are dominantly white to l i g h t grey i n c o l o u r , g i v i n g them a resemblance to limestone. They are almost u n i v e r s a l l y f i n e l y textured and t h i n l y bedded.  M i c r o s c o p i c a l l y these rocks consist dominantly  o f i n t e r l o c k i n g and intergrown quartz and f e l d s p a r  (49) g r a i n s , with which i s always associated a c e r t a i n amount of s e r i c i t e and carbonate, that occurs as a binder or matrix f i l l i n g the comparatively s l i g h t amount of i n t e r s t i t i a l space throughout the rock mass. The dolomites much resemble the f i n e - g r a i n e d , g r e y i s h q u a r t z i t e s i n appearance and are s i m i l a r to them i n hardness.  They are dominantly l i g h t gray to y e l l o w -  i s h i n c o l o u r , and are nearly everywhere t h i n l y bedded. The dolomites also contain i n t e r c o l a t e d seams of chert and q u a r t z i t e s . The shales include g r e y i s h to black, t h i n l y bedded, f l a k y , non-calcoreous members, as w e l l as other l e s s t h i n l y bedded black, s o f t shales which r e a d i l y decompose to form black mud. Although the rocks are highly f o l d e d and f a u l t ed, metamorphism i s not pronounced i n the d i f f e r e n t members o f the group; they have nowhere a schistose or g n e i s s o i d structure and seldom possess a s l a t y  cleavage.  They are thus very d i f f e r e n t i n t h i s respect to the Yukon group. Occasional dykes and small i n t r u s i v e masses o f diabase p i e r c e these rocks, i n p l a c e s , and since the dykes r a r e l y extend up i n t o the o v e r l y i n g rocks, the diabase i s probably also o f Cambrian age.  Palaeozoic  Pre-Middle  (50) No f o s s i l s were found in t h i s group o f rocks, but the beds underlie Devono-Cambrian limestones in which Middle Cambrian f o s s i l s were found.  Below t h i s  Middle Cambrian horizon several hundred f e e t of  litho-  l o g i c a l l y s i m i l a r , but u n f o s s i l l f e r o u s limestones and dolomites, which i n a l l p r o b a b i l i t y represent the Lower Cambrian, occur and underlying these beds unconformable* (1) occur the T i n d i r rocks described above.  Caimes  the opinion that the T i n d i r rocks are e n t i r e l y  i s of  Pre-  Cambrian or that t h i s group includes both Lower Cambrian and Pre-Cambrian members. I t i s considered that these rocks (2) may belong to the B e l t Terrane o f B r i t i s h Columbia.  I t also appear  that the Pre-Cambrian i s e x t e n s i v e l y developed i n port i o n s o f Yukon, and that these rocks are d i v i s i b l e  into  an upper but s l i g h t l y metamorphosed d i v i s i o n , the T i n d i r rocks, and a lower h i g h l y metamorphosed d i v i s i o n , the "Yukon group. Cambrian - S i l u r i a n .  (3)  Rocks o f t h i s age are described by C a i m e s , and are only known, so f a r , to occur i n t h i s one l o c a l ity.  He f i n d s that these rocks are r e s t r i c t e d to the  ( 1 ) Catrnes D.D. * Op. C i t l " P7"56l * ( 2 ) Daly R.A. G.S.C. Mem. #38, PP.179-191 1912. S c h o f i e l d S . J . "Reconnaissance i n East Kootenay,B.C. G.S.C. Sam.Rp. 1912 PP. 221-225. ( 3 ) Caimes D.D. "Yukon-Alaska I n t e r n a t i o n a l Boundary between Porcupine and Yukon R i v e r s , " G.S.C. Mem 67. P.58.  (51) higher mountainous t r a c t s o f Keele and O g i l v i e mountains. The rocks consist o f white t o l i g h t grey limestones and dolomites.  They are dominantly  crystalline  and i n places beds of p a r t i c u l a r l y good marble occur. I n texture these limestone-dolomite rocks vary from f i r m dense, dolomites to coarsely c r y s t a l l i n e almost pure limestones.  They also appear somewhat massive.  The dolomites are considered to have been derived from the limestone. In a few places, g r e y i s h , y e l l o w i s h , to nearly black shales are i n t e r c a l a t e d with these limestonedolomite beds.  They a r e , however, o f minor importance.  Cairnes found i t p r a c t i c a l l y impossible and Impracticable to separate the S i l u r i a n , Ordoviclan and Cambrian beds.  They are a l l much f o l d e d and f a u l t e d .  These limestone-dolomite rocks are o v e r l a i n by Devonian limestones, ^hich a r ; , i n turn,  overlain  by Carboniferous limestones, cherts and r e l a t e d rocks. The f o s s i l s obtained from the limestones gave agee from Cambrian to S i l u r i a n , and the Cumbrian, Ordovician, and S i l u r i a n horizons were r e c o g n i z a b l e . Devonian. (1)  Cairnes  Limestones o f t h i s age have been described by from the Keele and C g i l v i e mountains where they  are i n t i m a t e l y associated with the Cambro-Silurlan group  (52) o f limestones and dolomites. Shale-chert rocks ranging in age from Ordovi(1) elan to Devonian have been described by Caimes  and  C o c k f i e l d from many l o c a l i t i e s i n Yukon r e g i o n . The limestone beds resemble very c l o s e l y those o f the Cambro-Silurian and f o s s i l s , alone, serve as the distinguishing feature.  They are more homogenous and  darker i n appearance, the colour being t y p i c a l l y dark, bluish g r e y .  They are also somewhat c r y s t a l l i n e .  T h e i r age i s d e f i n i t e l y f i x e d by f o s s i l remains and the rocks have been c o r r e l a t e d l i t h o l o g l c a l l y with known areas o f Devonian limestone i n Alaska. The shale-chert s e r i e s consists dominantly o f shales and cherts which are p r e v a i l i n g l y c l o s e l y and f i n e l y interbedded. shaly c h e r t s .  They vary from cherty shales to  The cherts are g e n e r a l l y dark grey to  black i n colour &nd the shales are grey to black or b l u i s h black i n colour, the darker beds being decidedly calcareous i n character. Devonian f o s s i l s have been found i n these shalechert beds and they d i r e c t l y o v e r l i e middle or lower Cambrian limestone beds.  They a r e , i n turn, o v e r l a i n  by Carboniferous shales.  Shale-chert beds, probably  s i m i l a r to these beds, have been described from various (1)  Caimes D.D.  Op*Cit.  P.  83  (53) (1) places i n Yukon but Caimes a f f o r d s the most accurate data, to d a t e , as regards t h e i r age.  They have been,  by C a i m e s , r e f e r r e d to the Cache Creek s e r i e s o f B r i t i s h Columbia. Carboniferous. Rocks ascribed t o the Carboniferous period have an extensive developement i n Yukon.  However,  there has been considerable d i f f i c u l t y i n determining t h e i r age.  (I)  Cairnes a f f o r d s us the f i r s t c l e a r intimation o f t h e i r age, i n h i s work along the 141st. meridian. Here he describes two g e o l o g i c a l formations, one the shale group, and the other the limestone chert group. The shale group i s , apparently? only known i n the v i c i n i t y o f the 141st. meridian. This shale group consists dominantly o f shales but includes also c l a y s , c h e r t s , calcareous sandstones, and t h i n l y bedded limestones.  The whole group I s domin  antly dark i n c o l o u r . Since these shale beds r e s t upon Devonian shales and cherts i t would seem quite p o s s i b l e that R l s s i s s i p p i a n members are also included i n the shale group, unfortunately f o s s i l remains were not found. ( 1 ) Cairnes D.D,  Op. C i t . P. 83  (54) The limestone-chert group consists mainly o f limestone and c h e r t , but includes also occasional beds o f dark shale, calcareous sandstone and cherty conglomerate.  The limestone beds are quite c r y s t a l l i n e and  range from white to grey to almost black i n c o l o u r . These beds contain both Pennsylvanian and Mississiplan f o s s i l s .  They o v e r l i e the Devonian limestones  and are o v e r - l a i n by Pennsylvanian beds. Another group o f rocks the Nation River format i o n , was described by Caimes from t h i s same area. These consist dominantly o f conglomerates,  sandstones,  and shales but include also occasional beds o f  limestone.  The pebbles o f the conglomerate consist dominantly o f chert and are small ( 1 inch) in s i z e .  The sandstones  are c h a r a c t e r i s t i c a l l y g r e y i s h to brownish, medium t e x tured, hard, f i r m rocks.  The shales are dominantly  g r e y i s h to y e l l o w i s h i n colour and range i n character from f r i a b l e to hard and somewhat s l a t y , and from quite f i n e to coarse and arenaceous*  The limestones are l i g h t  g r e y , s e m i - c r y s t a l l i n e to c r y s t a l l i n e beds and occur g e n e r a l l y as thin beds i n t e r c a l a t e d with the more arenaceous and a r g i l l a c e o u s  sediments.  Imperfect plant remains were found, thus p l a c ing the beds as o f p o s s i b l e Carboniferous age. A conglomerate consisting of a f i r m , somewhat dense, f i n e l y t e x t u r e d , reddish, a r g i l l a c e o u s matrix,  (55) i n which are embedded angular to sub-angular pebbles and boulders ranging i n s i z e from microscopic t o 3 o r 4 f e e t i n diameter.  The matrix appears to have approx-  imately the composition o f a boulder c l a y , and the g r e a t e r number o f the pebbles and boulders are composed o f limestone or dolomite, but some were noted composed o f e t h e r sediments such as sandstone, conglomerate, and shale. The p r e v a i l i n g red colour of the matrix i s due mainly at l e a s t to the considerable amount o f i r o n contained i n the matrix which has i n places the appearance of hematite o r e .  The conglomerate i s quite un-  s t r a t l f i e d and has the general appearance o f a c o n s o l i dated and i r o n - s t a i n e d boulder c l a y .  The pebbles and  boulders are i r r e g u l a r l y d i s t r i b u t e d and are o f t e n q u i t e i s o l a t e d and completely surrounded by the matrix,  instead  o f r e s t i n g upon one another as i n the case o f a normal conglomerate. This conglomerate i s undoubtedly o f origin.  terrestrial  I n general composition,this conglomerate,  re-  sembles boulder c l a y more than i t does s l i d e m a t e r i a l , but on the other hand, i t s p r e v a i l i n g reddish c o l o u r , and the f a c t that t h i s conglomerate has not been described from other portions o f Alaska o r Yukon, and i s thus probably net very extensive would tend to disprove the g l a c i a l theory o f o r i g i n .  Although s t r i a t e d pebbles  (56) (1) were not found Cairnes thinks they might occur. Pebbles having f a c e t t e d s u r f a c e s , much resembling " s o l e d " pebbles were noted to be somewhat p l e n t i f u l ,  The con-  glomerate i s considered to be too extensive f o r s l i d e material.  This taken i n conjunction with the thickness  o f the conglomerate Cairnes thinks rather favours the glacial  theory. This conglomerate o v e r - l i e s the Devono-Cambrian  limestone-dolomite beds and appears to o v e r l i e Carboniferous shales and Devono-Crdovician shale-chert group and to s t r a t l g r a p h i c a l l y correspond to the Nation River formation.  The conglomerate was thus probably formed  about Carboniferous time, and may correspond to the PermoCarboniferous t i l l i t e s or conglomerates considered t o be o f g l a c i a l o r i g i n , that occur i n South A f r i c a , A u s t r a l i a , I n d i a and other parts of the world. Along the boundary l i n e Cairnes found three f a i r l y d e f i n i t e l y i d e n t i f i a b l e Carboniferous h o r i z o n s . The lowest i s represented by M i s s l s s i p i a n f o s s i l s from the lower p o r t i o n of the limestone-chert group.  The  next more recent horizon i s represented by Pennsylvanian f o s s i l s obtained from the shale group and the upper port i o n of the limestone-chert group.  The most recent  horizon i s represented by f o s s i l s from the Nation River ( 1 ) Cairnes D.D. "Yukon-Alaska Boundary"between Porcupine and Yukon r i v e r s , " G.S.C. Mem 67.P.92, 1914.  (57) formation which i s o f Upper Pennsylvanian or possibly Permian age. Limestones, cherts, and r e l a t e d rocks that l i t h o l o g i c a l l y resemble the members o f the llmestone(1) (2) chert group are described by McConnell.  Caimes  i s of  the opinion that the members of t h i s group are also probably included in the Braebum limestones which are ex(3) t e n s i v e l y developed in Yukon and northern B r i t i s h (4) Columbia and are dominantly o f Carboniferous age, but . (5) may include also Devonisn members.  -  Cockfield, a f t e r  the f i e l d season of 1929, i s o f the opinion that he has s u f f i c i e n t f o s s i l evidence, which was h i t h e r t o l a c k i n g , to place the Braebum limestones high up i n the Mesozoic succession. The w r i t e r f e e l s that the Braebum limestones should be described here rather than be placed i n an i n d e f i n i t e period o f the Mesozoic e r a .  These limestones  are g e n e r a l l y s u b - c r y s t a l l i n e , i n places approaching marble, but i n others quite f l a g g y and a r g i l l a c e o u s or ( 1 ) McConnell R . d . An.Rp.G.S.C. Vol.XV,19u2, 31A-34A. ( 2 ) Cairnes D.D. "Yukon-Alaska Boundary," G.S.C. Mem. 67 F. 103. 1914. ( 3 ) Caimes D.D. "Preliminary memoir on Lewes and Nordens k i o l d Rivers coal d i s t r i c t , " G.S.C. Mem 5. 1910 PP.28,29. ( 4 ) Cairnes D.D. " A t l i n d i s t r i c t , B r i t i s h Columbia." G.S.C. Mem 37 1912, PP. 53-54. ( 5 ) C o c k f i e l d W.E. Personal Communication 1930.  (58) even s i l i c e o u s . in colour.  They are commonly white to l i g h t bluish  (1)  Cairnes  s t a t e s that " t h i s limestone appears  to be the same as that o f the Upper Cache Creek s e r i e s , found to the south in the Conrad Mining d i s t r i c t , and t h e r e f o r e of Carboniferous age.  The evidence a f f o r d e d  by the f o s s i l s c o l l e c t e d has been of  ¿.n i n d e f i n i t e  character, and the i n f e r e n c e that the t^o formations are of the same age has bean mat - mainly on H t h o l o g i c a l grounds." As previously stated C o c k f i e l d f e e l s c e r t a i n that recent f o s s i l evidence - i l l place these limestones i n the upper Mesozoic e r a .  I f t h i s happens i t *.vill help  g r e a t l y in u n r a v e l l i n g the v o l c a n i c complex. Limestones s i m i l a r to the Braeburn limestones have been described by C o c k f i e l d from the Whltehorse D i s t r i c t and as regards t h e i r age he s t a t e s : - " T h e evidence as to the an;o o f the limestones i s very u n s a t i s f a c t o r y . I t i s how-aver, quite possible that linastones belonging to more than one g e o l o g i c period have been included. The most d e f i n i t e evidence to date i s the f i n d i n g o f the genus f u s i l i n a by 9.M. Dawson,  vhich would demonstrate  that part at l e a s t of the limestone i s Carboniferous. Some evidence has been presented to show that Devonian and T r i a s s i c faunas may also be represented, h-r-.t as y e t IT.)" C o c k f i e l d W.E. and B o l l AjlH "Whitehorse d i s t r i c t , Yukon." G.S.S. Mem. 150 P.14 1926.  (59) no progress has been made i n subdividing the limestone i n t o d i f f e r e n t formations.  The evidence as a whole i s  too meagre to permit o f s t a t i n g that Devonian and T r l a s s i e are r e p r e s e n t e d . "  (1)  C o c k f i e l d describes  cherty q u a r t z i t e s , black  s l a t e s , b i o t i t e s l a t e s and limestone from Windy Arm and Tagish l a k e .  These beds extend toward A t l i n and are  f o l l o w e d by g e n e r a l l y c r y s t a l l i n e limestone, from which fragments of f o s s i l s are obtained.  Without f u r t h e r  statement he r e f e r s the limestone to the Upper Carboniferous or T r i a s s i c thus placing the q u a r t z i t e s ,  slates  and the other band o f limestone as.Pre-Upper Carboniferous. Rocks ranging in age (2) from Ordoviciah t o Car oni f e r o u s have been described area.  from the Dezadeash Lake  They consist o f dark, coarsely-bedded  argillites  seldom strongly cleaved, but i n some instances  consider-  able mica has developed and they pass i n t o a s c h i s t . These rocks also contain greyish q u a r t z i t e and some conglomerate but no o limestone was found. angles from 50-85.  They dip at steep  No f o s s i l s were found.  The only  evidence as to t h e i r age i s that they o v e r l i e Pre-Cambrian ( ? ) s c h i s t s and are cut by g r a n i t i c (1) Cockfield  intrusives.  E x p l o r a t i o n s in 6. Yukon," 6.S.6.**** Sum. Rp. 1922. ( 2 ) C o c k f i e l d *.?.E. "Dezadeash Lake Area, Yukon," G.S.C. SHm. Rp. 1927.  (60)  Since the age o f the g r a n i t i c i n t r u s i v e s i s assumed as Jurassic, C o c k f i e l d places these sediments as ranging from Crdoviclan to Carboniferous i n age.  UBC Scanned by UBC Library  (61) MESOZOIC  ROCKS.  The most wide-spread sedimentary horizon o f the Meaozoic era i s represented by sediments ranging i n age from Jurassic to Cretaceous.  This horizon appears  to be more wide spread i n Southern Yukon than i n the northern p o r t i o n . Igneous rocks of the Mesozoic era are very ext e n s i v e l y wide-spread throughout Yukon and w i l l be described i n some d e t a i l under the heading "igneous Rocks." Triassic. Limestone occurring i n patches and bands i n (1) a n d e s i t i c rocks has been described by C o c k f i e l d .  These  bands are seldom more than 5C0 f e e t wide and the bedding i s i n most places obscure, and d i f f i c u l t or impossi b l e to d e t e c t .  The limestone i s grey and compact, and  l a r g e l y , i f n o t , wholly r e c r y a t a l l i n e .  From the poor  f o s s i l s c o l l e c t e d there would appear to he two bands o f limestone, one o f Carboniferous ( ? ) age and the other of T r i a s s i c ( ? ) age.  Phase cannot be separated but i t  is  probable that Mesozoic limestone may be present. C o c k f i e l d also describes a s e r i e s o f conglome r a t e s and a r g i l l i t e s from t h i s same area.  The conglom-  e r a t e s are massively bedded with cobblas and boulders o f ( 1 ) C o c k f i e l d W.K. " 3 L .iSt t. C l e. Sum. Salmon Rp.niv^r 1928.area, Yukon,"  (62) g r a n i t e , andesite and schistose rocks i n a t u f f a c e o u s matrix.  A few exposures of dark grey to black  i t e s were found.  argill-  The a r g i l l i t e s have been j o i n t e d and  sheared so that the bedding i s  indistinguishable.  F o s s i l s obtained from the a r g i l l i t e s c o r r e l a t e d the beds as belonging to probable Upper T r i a s s i c . The Laberge beds have been determined i n Whitehorse d i s t r i c t as o f probable Lower Jurassic age to Middle Jurassic age.  I t seems apparent that  argillites  above do not -belong to the Laberge beds, but c o n s t i t u t e an underlying formation.  "Occasional f o s s i l s that were  b e l i e v e d to be T r i a s s i c forms have been h e r e t o f o r e found i n southern Yukon, i n a l l cases i n limestone, but t h e i r poor s t a t e o f preservation prevented a d e f i n i t e age determination.  I t would now appear to be f a i r l y  d e f i n i t e l y e s t a b l i s h e d that marine T r i a s s i c i s much more widespread i n southern Yukon than was formerly b e l i e v e d to be the case.  I t i s also p o s s i b l e that some  marine T r i a s s i c has been included with the Laberge beds i n other s e c t i o n s . Jurassic. Sedimentary rocks have been assigned to the Jurassic period by C o c k f i e l d i n the Whitehorse Here C o c k f i e l d f i n d s these rooks e x t e n s i v e l y  (1)  District.  developed  ( 1 ) C o c k f i e l d Y'.E. and B e l l A.B. "Whltohorse d i s t r i c t , " Yukon," G.S.C. Mem. 150 p.15 1926.  (63) i n the eastern ha^f o f the d i s t r i c t .  They occur as  l o n g , somewhat narrow b e l t s with a trend a l i t t l e  east  of north and south o f west, p a r a l l e l to the Coast range,  (i)  Caimes  has determined t h e i r thickness as between 5,000  and 6,000 f e e t .  These rocks consist domlnantly o f v o l -  canic c l a s t i c s , t u f f s , b r e c c i a s , and conglomerates. Interbedded with the t u f f s are considerable  thicknesses  o f marine shales and a r g i l l i t e s i n which tufiaceous m a t e r i a l i s an important c o n s t i t u e n t .  In a few places  thin beds o f . d s r k , impure limestone are interbedded with the bedded t u f f s . This group of rocks C o c k f l e l d has c a l l e d the Laberge s e r i e s and includes i n the s e r i e s the Tantalus conglomerate.  C a i m e s , In h i s repcrt on the Conrad and  Whitehorse mining d i s t r i c t s , groups these two formations under the name Tutshi  s e r i e (2) s.  In Wheaton d i s t r i c t  where the best exposures  o f t y p i c a l l y marine sediments occur, a three f o l d d i v i s ion o f the Laberge beds was recognized and i f  the Tanta-  lus conglomerate be included, a f o u r - f o l d d i v i s i o n was determined.  The lower beds of the Laberge s e r i e s con-  s i s t o f arkoses, t u f f s with shales and conglomerates. The middle members are composed o f shales,  sandstones  and arkoses; and the upper beds consist c h i e f l y of ( 1 ) Caimes D.3. "Wheaton t r i c t , Yukon," G.S.C. Mem 21, d i s 1912. ( 2 ) C a i m e s D.D. Op. C i t .  (64) sandstone*  Overlying those d i v i s i o n s i s the Tantalus  conglomerate which i s com osed o f conglomerate,  shale,  sandstone, and c o a l . C a i m e s notes that these d i v i s i o n s are only approximate and that the thickness o f each v a r i e s .  In  the lower beds the arkoses are g e n e r a l l y l i g h t to dark grey or pale greenish, but occasional red beds are found. They have a dense texture and are f i r m , compact rocks, which occur i n heavy, massive beds, so that the s t r a t i f i c a t i o n i s i n many cases only d i s t i n g u i s h a b l e from a distance.  Associated with the arkoses are t u f f s which  so resemble them that i t i s g e n e r a l l y d i f f i c u l t to  tell  them apart. More than h a l f the lower beds of the laberge s e r i e s consists c h i e f l y o f these arkoses and t u f f s but the upper p o r t i o n contain a considerable developement o f conglomerate and s h a l e .  The conglomerate occurs in  t h i c k , massive beds and consists o f m a t e r i a l varying widely i n s i z e .  The pebbles and boulders range i n s i z e  from that o f sand grains to 6-8 inches, o r more in d i a meter and are mainly e i t h e r a n d e s i t i c fragments derived from the "Older V o l e a n i c s " o r pebbles i d e n t i c a l i n comp o s i t i o n with the Coast Range g r a n o d i o r i t e s .  The shales  range from l i g h t grey to almost black, and usually form successive form colour.  20 or SO f e e t thiek and eacb o f a uni-  (65) The middle beds consist c h i e f l y of shales similar to those described above, but characteristically iron-stained and generally presenting a red appearance. When broken, however, they are seen to be grey to black, hard, dense rocks.  These rocks occur in l a y e r s , with  associated arkoses and sandstones, but the shales predominate. The upper beds consist almost e n t i r e l y  of  medium-textured, somewhat f r i a b l e sandstones p r e v a i l i n g l y g r e y i s h , y e l l o w i s h , o f l i g h t brown, and occur i n heavy, nasslve beds.  These d i f f e r g r e r t l y from the hard,  dense, compact rocks noted i n the middle beds. In the Wheaton d i s t r i c t the more t r u l y  clastic  members o f the group occur i n a b e l t f o l l o w i n g the marg i n o f the Coast range, and the members composed l a r g e l y o f v o l c a n i c m a t e r i a l a p p a r e n t l y increase i n importance to the north and e a s t .  (1)  In the Whltehorse d i s t r i c t  the t u f f s o f the  Laberge s e r i e s are o f two main t y p e s ; bedded and 2 . medium-grained, massive.  1.fine-grained These two v a r i -  e t i e s occur intorbedded, but In places there i s a t h i c k ness of s e v e r a l hundred f e e t o f one v a r i e t y without any admixture o f the o t h e r .  The bedded t u f f occurs i n some-  what g r e a t e r abundance than the non-bedded. ( 1 ) C o c k f l e l d W.^. Yukon," and B e l l G.S+C. A.H. "Whitehorse trict, Mem 150 P.16d i s1926.  (66) The non-bedded t u f f i s not e a s i l y  distinguished  from an igneous reck sueh as diabase o r b a s a l t . an important member o f the Laberge s c r i e s .  It  is  This rock  has been described as a sandstone, arkose, or greywacke. I t I s f i n e t o medium-grained and v a r i e s i n colour from l i g h t to dark grey and from grey to green.  In some  cases i t contains mica, and to the unaided eye appears to have the composition of a g r a n i t e or d l o r i t e .  It  is  interbedded with f o s s i l - b e a r i n g shales o r a r g i l l i t e s and with more o r l e s s f i n e l y laminated t u f f s * In the Whitehorse d i s t r i c t the Laberge  series  appears to o v e r l i e the Palaeozoic limestone with angular unconformity*  The contact o f the t u f f s with the Coast  Tange i n t r u s l v e s i s o f an extremely undulating nature and the f a c t that l a r g e apophyses are connected with the main body o f the i n t r u s i v e prove beyond doubt that the t u f f i s intruded by the granod5orite.  Dykes o f  g r a n i t i c rocks, probably connected with the l a r g e r i n t r u s i v e b o d i e s , cut the bedded t u f f s and the greenstones with which the l a t t e r are a s s o c i a t e d . F o s s i l s w^re found i n the shale beds o f the Laberge s e r i e s In Whitehorse d i s t r i c t . Here i t has been (1) stated "that on the whole f o s s i l s ere o f aomewhat rare occurrence." ITT^ki-ield  and B e l l A.R, "Whitehorse d i s t r i c t , Yukon," G.S.C* Mem 150 P.21 1926.  (67) The f o s s i l s from this d i s t r i c t indicate the presence of strata ranging i n age from Middle Lias to I n f e r i o r Oolite, that i s o f strata of various stages, exclusive of the oldest, of the Lower Jurassic and e a r l i e s t Middle Jurassic. F o s s i l s have been c o l l e c t e d from the Laberge bads i n Wheaton, A t l l n , Whitehorse and Tantalus areas. I n the c o l l e c t i o n s f r o n the Tantalus area, the specimens  (1)  were regarded as Jurassic or Cretaceous,  but these  species arc new regarded as Jurassic forms.  Fossils  c o l l e c t e d i n the A t l l n d i s t r i c t were reported on by Stanton as f o l l o w s : "These may p o s s i b l y be T r i a s s i c , but I think i t more probable that they are e a r l y Jurassic.  is)  They are c e r t a i n l y not as l a t e as the Cretaeeous."  In the Wheaton and Whitehorse d i s t r i c t s C a i m e s  reports  numerous specimens which were regarded as p o s s i b l e young i n d i v i d u a l s o f Prioncyclus w o o l g a r i . and B e l l  Cockfield  are o f the opinion t h a t ; " I n view of the more  p o s i t i v e evidence a f f o r d e d by other c o l l e c t i o n s  of  f o s s i l s , i t seems h i g h l y probable that the t e n t a t i v e i d e n t i f i c a t i o n c f Prioncyclus woolgari by Whiteaves should be disregarded.  Thus i t appears to be very w e l l  established that the Laberge beds range i n age from ( 1 ) Caimes D.D+ "Lewes and Nordenskiold Rivers Coal D i s t r i c t . * 6.S.C. Mem 5. PP. 34-35 ( 2 ) G w i l l i n J.C. G.3.C. An.Rep. Vol X I I , P t . 3 , PP 23-27 189S. ( 3 ) C o c k f i e l d W.E. and B e l l A.H. "Whitehorse d i s t r i c t , Yukon." G.S.C. Mem 150 P.22 1926.  (68) middle Lower Jurassic to lower Middle Jurassic.  These  rocks have formerly been correlated as of Cretaceous age. The Tantalus conglomerates have been included as 4 subdivision of the Laberge beds i n t h i s thesis. The conglomerates are rather wide spread in Southern Yukon and are of economic interest since they are h o r i zon markers f o r the coal seams of Yukon. These conglomerates consist chiefly of massive beds of conglomerate, but also contain sandstones, shales, and coal seams. Caimes in the  Their thickness as measured by  Wheaton d i s t r i c t i s in the neighbour-  hood of 1,800 f e e t .  The conglomerates d i f f e r from a l l  others of Yukon i n that they are composed almost e n t i r e ly of pebbles of quartz, chert and s l a t e , the pebbles being generally cemented by a siliceous matrix.  The  component pebbles are remarkably uniform in s i z e ,  rarely  exceeding three inches in diameter and f o r the most part being between 1 and 2 inches in diameter.  The associat-  ed sandstone consists of thesame materials as the conglomerates, but In a f i n e r state of d i v i s i o n .  The shales  occur c h i e f l y in the v i c i n i t y of the coal seams and are generally f i n e l y textured rooka with a s l a t y cleavage. The Tantalus conglomerate o v e r l i e s , to a l l appearance, conformably, the Laberge s e r i e s .  Fossil  (69) (1)  plants from theeoal seams  place the age of the con-  glomerate as Cretaceous.  (2)  F o s s i l plants collected by Caimes  from the  Wheaton d i s t r i c t placed the age of the conglomerate as Jurassic.  In view of the f a c t that the beds were 11th-  o l o g i c a l l y similar to the Kootenay beds and contained coal seams and that some forms of the f o s s i l plants had been reported from the Kootenay formation, Caimes classed these beds as probably belonging to the Cretac(3) +ous.  Cockfleld and B e l l ,  however, consider that;  "The plant evidence given above seems to corroborate the animal evidence obtained from the Laberge beds, and there can be l i t t l e doubt that the Laberge beds and Tantalus conglomerate are both of Jurassic age, and i t would appear that the e a r l i e r determinations of f o s s i l s are to be regarded as extremely doubtful in the l i g h t of the more exact evidence now presented." Cretaceous. Rocks of this age have been described from (4) the Upper White River d i s t r i c t ,  they consist to a great  extent of dark or banded shales and a r g i l l i t e s with which are interbedded a large proportion of greywacke ( l ) Caimes D.D. "Lewes and Nordensklold Rivers Coal d i s t r i c t , " G.S.C. Mem 5 ^ . 3 8 . 1910. (2) Caimes D.D. G.S.C. Sa*. Rp. 1915 P.41. ( 3 ) Cockfleld W. E. and B e l l A.H. "Whitehorse d i s t r i c t . " G.S.C. Mem 150 P.23 1926. ( 4 ) Caimes D.D. "Upper Whit* River d i s t r i c t , " G.S.C. Mem 50 P.84 1915.  (70) and smaller amounts of conglomerate and sandstone, the entire series being notably more siliceous than the underlying Carboniferous beds.  (1)  Similar rocks were found by Calmea Yukon-Alaska boundary.  along the  The l i t h o l o g i c a l descriptions  are similar. These sedimentary formations were found to l i e conformably upon the Perms-Carboniferous ( ? ) beds and in places i t was d i f f i c u l t to determine between them. Fossils, although rare, were found and they place the age of the beds as Lower Cretaceous. Formerly the Laberge series and the Tantalus conglomerate were considered of Cretaceous age but the Laberge series i s d e f i n i t e l y of Jurassic age as shown. (2) The Tantalus conglomerate Cockfield  thinks may be  younger than Jurassic but i t rests conformably upon the Laberge series and f o s s i l evidence, so f a r , appears to indicate a Jurassic age.  ( 1 ) Caignes D.D. "Yukon-Alaska Boundary," G.S.C. Mem 67, PP. 105-106 1914. ( 2 ) Cockfield W.B.Personal Communication  1930.  (71)  TERTIARY Tertiary sedimentary rocks have been described from a few areas namely the Upper White r i v e r , mile r i v e r , Kluane and Elondyke d i s t r i c t s .  Sixty-  They have  also been described from the Porcupine, Peel and Frances rivers. These beds comprise mainly loosely or only partl y consolidated sandstones, shales clays and conglomerates.  The sandstones are prevailingly greyish to yellow-  ish and brown in colour, and the shales and clays are dominantly some l i g h t shade of grey, green or blue, but some quite black strata occur.  The shale i s a dense,  compact rock containing abundant f o s s i l wood, though no other f o s s i l s could be found.  The sandstone i s a s o f t ,  f r i a b l e , coarse sandstone or arkose, consisting of quartz and decomposed feldspar with abundant ferruginous matter. These sandstones contain a few scattered pebbles of quartz, quartzite, or schist, and towards the upper portion of the beds the pebbles become more numerous, the rock grading into a conglomerate.  Where these beds have  been intruded by volcanic rocks they have become indurated probably due to the i n f i l t r a t i o n of siliceous materi a l s from the volcanics. A l l the beds are s o f t and d e c r e p i t , tc to forr: sand and clay beds.  readily  Tha^e r e e l s ^re pi-iv,.ijJngly  (72) f l a t l y i n g , and i n most places have been only s l i g h t l y disturbed by earth movements.  They have been extensive-  l y invaded by more recent volcanies including members of both the r h y o l i t e - l a t i t e group and the newer volcani c s , which pierce or o v e r l i e them wherever they are exposed.  Their occurrence in scattered patches on the  upland suggests that they participated in the movements of the Yukon Plateau p r i o r to i t s planation. (I) Prindle  i s of the opinion that the lower beds  of these sediments are usually fine-grained but become coarser towards the top and the upper beds are almost always conglomeratic.  The l i g n i t e does not appear to  be confined to any particular horizon in these beds. Though the absence of f o s s i l s in these beds makes their age d i f f i c u l t to determine, their structural relations show they participated in the movement of Yukon plateau p r i o r to i t s u p l i f t and subsequent plana-  (2)  tlon.  Spurr  believes that the u p l i f t and planation of  the Yukon plateau was probably contemporaneous with the deposition of Miocene strata in lower v a l l e y of Yukon r i v e r , and that the beds are Pre-Miocene.  These rocka  are probably continuous with the Tertiary rocks described ( 1 ) Prindle L.H. "The Forty mile quadrangle," U.S.G.S. B u l l . 375, 1909 PP. 23*26. ( 3 ) Spurr J.E. "The geology of the Yukon gold d i s t r i c t , Alaska," U.S.G.S. An.Rp.Pt.3,1898, PP. 260-263.  (73)  (1) by McConnell  from the Klondike region as the Kenai  aeries and possibly equivalent to certain beds in the Fortymile d i s t r i c t which, (2) from f o s s i l evidence, have been referred to-that age. These correlations place the rocks as Upper Eocene.  Since, also, the Kenai beds contain seams of  l i g n i t e , i t i s customary to include in that formation a l l Tertiary beds containing coal.  I t would thus seem  possible that rocks more recent than Eocene have bran in places Included in the Kenai a e r i e s . The Kenai sediments in most places represent deposits l a i d down in separate basins of deposition, and the plant remains which they contain show that most of them at least are of fresh-water o r i g i n .  The  l i g n i t e seams in the Kenai series are not confined to any particular horizon, but occur in a l l positions from top to bottom of the s e r i e s .  This i s just what might  be expected, considering that the Kenai beds are believed to have been deposited in unconnected basins, in which case, the coal seams would not be formed in a l l the basins simultaneously, nor would they occupy similar positions in the series in d i f f e r e n t l o c a l i t i e s .  ( 1 ) McConnell R.G. G.S.C. An.Rp. 1901 pp. 23B-24B. ( 2 ) Prindle L.M.  O p . C i t . pp. 23-26  (74) QUATERNARY  and  RECENT.  These deposits are very extensive i n Yukon and in places quite thick.  They are generally con-  fined to the valleys and lowlands; as a rule they are lacking on the upland surfaces.  These deposits are  of g l a c i a l , f l u v i a l , and lacustrine o r i g i n and consist of sand, gravel, s o i l , Kilt, clay, boulder clay and a subordinate amount of volcanic ash.  (75)  IGNEOUS  ROCKS.  Pyroxenite and P e r i d o t i t e . Under t h i s heading a l l Pre-Mesozoic igneous rooks w i l l be described except those already described i n connection with the Yukon group*  These Pre-Mesozoic  Igneous rocks are comparatively wide spread and vary g r e a t l y i n composition, with possibly basic rocks p r e dominating* (1) Cairnes  describes a s e r i e s o f igneous rocks  along the Yukon-Alaska boundary as to include d i o r l t e s , andesites and diabases.  These occur as dykes,  and small i n t r u s i v e masses*  sills  They appear to be exten-  s i v e l y developed i n a s s o c i a t i o n with the sedimentary members o f the T i n d i r group (Pre-Middle Cambrian).  These  rocks, however, have not only invaded the T i n d i r sediments but i n a d d i t i o n they have intruded the members o f the Yukon group, as w e l l i n places as the lower beds o f the Devono-Carboniferous limestone-dolomites.  A l l the  i n t r u s l v e s examined i n t h i s r e g i o r proved to be diabases although Cairnes s t a t e s that other r e l a t e d roek types may be present.  Cairnes places t h e i r age as ranging  from Carboniferous to Pre-Cambrlan but thinks they ere domiaantly Pre-Middle Cambrian., ( 1 ) Cairnes b.D. "Yukon-Alaska Boundary," G.S.C. Mem 67, P. 109 1914.  Kf  (76) These diabases are p r e v a i l i n g l y g r e y i s h to dark  ?  green, f i n e to medium textured rocks which possess an  -*  o p h i t i c s t r u c t u r e , and may or may not be amygdaloidal i n character.  When amygdaloidal the anrygdules are  domlnantly f i l l e d with secondary minerals mainly quartz, c a l c i t e , z e o l i t e s , or c h l o r i t e .  On weathered surfaces  these i n t r u s i v e s are c h a r a c t e r i s t i c a l l y reddish to reddish brown, due to the o x i d a t i o n o f the i r o n - o r e minera l s which they contain and which i n some o f these rocks are somewhat abundantly d i s t r i b u t e d o r peppered through the rock mass.  (1)  Cockfield  describes a s e r i e s o f igneous rocks  from theUpper Beaver River a r e a .  These rocks are both  i n t r u s i v e and e x t r u s i v e , but occur c h i e f l y as s i l l s . Two types o f igneous rocks are found i n t h i s one an augite andesite, the other an augite  locality, dlorite.  The augite a n d e s i t e , i s a dark green, f i n e to aphanitic textured rock which under the microscope shows advanced a l t e r a t i o n to secondary m i n e r a l s .  This rock occurs both  as an i n t r u s i v e and as an e x t r u s i v e .  The augite  varys from coarse to f i n e t e x t u r e but i s o f habit.  dlorite  granitic  This rock contains augite and andesine.  The  augite andesite and augite d l o r i t e are considered o f post Ordovician-Devonian age since they are found (1) Cockfield W.E.  G.a.C. Sum. Rp.  1924  Pt. A  (77) intrusive into Pre-Ordovician-Devonian rocks.  Although  Cockfield found no evidence, he thinks that the andesite and diorlte are o f the same age. Pyroxenlte and peridotite rocks are described  (1)  from the Mhitehorse  (2)  and the Wheaton  districts.  Associated with these basic igneous rocks are v e i n s ed with serpentine and, i n some cases, coarsely l i n e amphibole.  fill-  crystal-  Talc and magnesite were a l s o found  associated w i t h ' t h e s e v e i n s .  The serpentine i s dark  o l i v e - g r e e n with a waxy l u s t r e and " pale bro.vn coating o f weathered products.  Some serpentine v e i n s have cent-  r a l veins o f c h r y s o t i l e asbestos.  Fibrous  serpentine  and t a l c occur i n narrow f i s s u r e s throughout the rock and on surfaces which appear s l i c k e n s i d e d . The p y r o x e n t i t e and p e r i d o t i t e rock as a whole i s very massive.  Fresh surfaces i n some cases appear  coarse-grained granular, and i n others no granular texture i s v i s i b l e .  The rock i s medium to dark grey o r  black, with, i n p l a c e s , a greenish t i n g e . surface i s coarsely p i t t e d and has a b r i g h t  The weathered reddish-  brown colour due to the presence o f i r o n o x i d e . Under the microscope the texture of the basic rocks was seen to be hynldiomorphic granular and rather coarse g r a i n e d .  The rock contains over 80 per cent and  11) Cockfield W.E. and Rell A.H. "Whitehorse d i s t r i c t , " G.S.C. Mem. 150 P. 10 1926. ( 2 ) Caimes D.D. "Wheaton d i s t r i c t , " G.S.C. Mem. 31, P. 49, 1912.  (78) up t o 95 per cent o l i v i n e .  Chromite i s prominent as  an accessory* probably making up 2 per cent o f the rock* Serpentine i s an important a l t e r n a t i o n product. The contact o f these rocks with other fonnil) ations was not seen. C o c k f i e l d i s o f the opinion that the p e r i d o t i t e s may be i n t r u s i v e .  (2)  them with the *Gold S e r i e s * .  Calmes  He c o r r e l a t e s was unable to  obtain i n the Wheaton d i s t r i c t any d e f i n i t e information concerning the age o f these rocks except that they cat members o f the Mt Stevens group (Yukon Group), but from t h e i r l l t h o l o g i c s i m i l a r i t y to the rocks i n o t h e r parts o f Yukon and i n northern B r i t i s h Columbia, he considers them to be probably o f about Devonian a g e . Older V o l c a n i c s . The rocks o f the Older Volcanles group are c h i e f l y andesites, diabases, and b a s a l t s .  Smaller  q u a n t i t i e s o f deep-seated, b a s i c rocks such as d i o r i t e , gabbro and amphlbollte have been included.  Areas o f  the Older Volcanics are rather wide-spread thoughout Yukon and have presented somewhat o f a problem as r e gards t h e i r age. These rocks are t y p i c a l l y compact, f i n e l y t e x t u r e d , and dark green, but red, brown, and blue types also occur.  They are p r e v a i l i n g l y p o r p h y r i t i c , with  f e l d s p a r c r y s t a l s i n an aphanitic ground-mass.  I n seme  ( 1 ) C o c k f i e l d W.E.& B e l 150 l A.H."Whltahorse district,"G.S.C. Mem. p.11 1926 ( 2 ) C a i m e s D.D. "Wheaton d i s t r i c t , " G . S . C . M e m . 3 1 1912.  (79) cases phenocrysts of hornblende and b i o t l t e may be discerned with the naked eye*  Iron i n the form o f  magnetite o r pyrite i s commonly present, and in many oases has oxodized, giving reddish or brownish colour to the rocks*  T u f f s and breccias occur i n may places.  Under the microscope these rocks are seen t o possess a v a r i e t y of compositions and o f  structures.  P l a g i o c l a s e i s always present and g e n e r a l l y occurs two g e n e r a t i o n s .  in  I t ranges from o l i g o c l a s e to bytownite  i n composition, but by f a r the :.ore common r l a g i o c l a s e s o r andesine or l a b r a d o r i t e .  The acid p l a g i o c l a s e  is  present c h i e f l y i n the groundmass o f the rocks. Orthoclase occurs i n a few cases as phenocrysts, and a l s o i n the groundmass.  The ferro-magnesiuxi minerals  include hornblende, b l o t i t e , pyroxene, and o l i v i n e . Both the common green hornblende and brown b a s a l t i c hornblende occur, but the former i s b,. f ^ r the more c common.  B l o t i t e i s a l s o common and i n some cases i s  the only ferromagnesium mineral p r e s e n t .  B i o t i t e and  hornblende occur t o g e t h e r , and e x i s t i n both generations.  Pyroxene, usually d i o p s i d e , i s p r e s e n t , but  seldom i n phenocrysts o f s u f f i c i e n t s i s e to be detected with the naked e y e .  O l i v i n e has been noted i n some o f  the augite a n d e s i t e s .  P y r i t e and magnetite are abun-  dant, i n many cases i n specks l a r g e enough t o be d e t e c t ed with the naked e y e .  (80) The a l t e r a t i o n o f these rocks in some cases is  w e l l advanced, and i n many cases masks the o r i g -  i n a l character.  C a l c i t e , c h l o r i t e , e p i d o t e and z o i z l t e  are abundant as secondary c o n s t i t u e n t s . The structure o f the rocks i s usually prophyr l t i c , and the phenocrysts, as d e s c r i b e d , c o n s i s t o f p l a g i o c l a s e and the ferromagnesium minerals. c r y s t s are as a rule f a i r l y abundant.  Pheno-  The groundmass  i s either holocrystalline or partly glassy. The rocks o f deep-seated character that have been included under the term "Older V o l c a n l c s " are on the whole greenish i n colour, massive and from f i n e to medium-grained.  These rocks Vary i n composition  but are g e n e r a l l y high i n ferromagnesium m i n e r a l s . Z o i z i t e and serpentine are common as a l t e r a t i o n products. (1) In h i s e a r l i e r work Calmes  separated the  "Older V o l c a n i c s " Into two groups, the Perkins group and the C h i e f t a i n H i l l v( 2o )l c a n i c s . This subdivision was l a t e r abandoned and both were included I n one group and c o r r e l a t e d with the Older Volcanics o f White (3) River d i s t r i c t . Portions o f the Older Volcanics are d e f i n i t e l y i n t r u s i v e i n t o the Laberge beds, and may, ( 1 ) Calmes D.D. "Wheaton d i s t r i c t , " G.S.C. Zei'i 59-64 19*12 ( 2 ) Cairnes D.D. G.S.cl Sum Hp. 1915* P. ( " ) Cairnes D.D. "Upper Vihite d i s t r i c t , " G.3.C. HetL.50 P.P7-9C.  (81) t h e r e f o r e , be considered as younger.  The s i m i l a r i t y  between the t u f f s o f the Laberge beds and those o f the Older Volcanlcs has been pointed out by C a l m e s , who b e l i e v e d th&t the period o f vulcanism represented by the Older Volcanlcs was i n some measure contemporaneous (1) with the d e p o s i t i o n o f the Laberge beds.  Gwilllm  o f the opinion thot these rocks may be c l o s e l y ed with the o r i g i n o f the sandstones.  is  connect-  He also noted  that "the change from t^o fragmental rocks to the porp h y r i a s and andesites i s g r a d u a l . " The o l d e r V o l c a n l c s , a r e , probably, a l l o l d e r than the g r a n i t i c i n t r u s i v o s .  Although some o f the  f l o w s arc -ore recent than the( 2 )Laberge s e r i e s with which - they come in c o n t a c t , C o c k f i e l d  i s of the opinion that  they are to a l a r g e extent contemporaneous with the Laberge s c r i e s and are probably of Lower and Middle Jurassic age; and that the t u f f s , which are so p l e n t i f u l in tho Labrrge s e r i e s , are to be a t t r i b u t e d to the same period o f vulcanlsm. Granitic  Intrusives. The g r a n i t i c I n t r u s i v e s form one o f the major  g e o l o g i c a l formations of Yukon, both in a r e a l e x t e n t , and i n importance as p o s s i b l e o r e - b r i n ^ e r s .  These rocks  ( 1 ) Gwillim J.C. "AtlJn Liining t r i cP.t , "28. G.S.C. An. Rp. I Pdt .i s"^hiteborse B. (2) Cockfield andVol B e lX l I A.H. district," G.S.C. Mem. 150 p. 29 1926.  (82) are exposed mostly i n southern Yukon where the Coast Range mountains trend northwesterly across the southern portion o f t h i s p r o v i n c e .  Considerable g r a n i t i c o u t -  l i e r s have been described but i t i s the general opinion that these i s o l a t e d outcrops are connected with the main body o f the i n t r u s i v e .  Thus i t i s the consensus  o f opinion that the Coast Range i n t r u s i v o s probably u n d e r l i e at l e a s t , the southern p o r t i o n o f the Yukon province. The rocks grouped under the head o f Coast Range i n t r u s i v e e present many d i f f e r e n t t y p e s , but they have i n general a g r a n i t i c h p b l t .  They are g e n e r a l l y  grey in c o l o u r , and f r e s h and unalteraa i n appearance. I n some c . s e s , however, pink f e l d s p a r i s present i n s u f f i c i e n t quantity to g i v e a pinkish cast to the rocks, but on the whole t h i s i s e x c e p t i o n a l .  The t y p i c a l rock  o f the Coast Range i n t r u s i v e s i s medium to  coarse-grain-  ed, with the e s s e n t i a l constituents v i s i b l e t o the naked eye.  L o c s l l y , phenocrysts o f f e l d s p a r , many exceeding  one to two inches, ere developed, and the rocks may be said to have a p o r p h y r i t i c t e x t u r e .  Quartz,  orthoclase,  p l a g i o c l a s e , ond ferronagnesiun minerals, i n nearly ever;, case hornblende and b i o t i t e ,  can r e a d i l y be ^ ? t e c t -  ed by the unaided e y e . When examined under the microscope, the majori t y of the sections are seen to contain quartz,  ortho-  (83) clase, m i c r o c l i n e , p l a g i o c l a s e , hornblende, b i o t i t e and, only i n some cases a u g i t e .  The amount o f  quartz  v a r i e s g r e a t l y , but i s mostly between 10 and 25 per cent f e l d s p a r s from 60 to 75 per cent, and the remainder i s hornblende and b i o t i t e , or augite*  Orthoclase and mic-  r o l l n e are as a rule about equal i n amount to the p l a g ioclase. andesine.  P l a g i o c l a s e i s most commonly o l i g o c l a s e  or  The hornblende and auglte^ i n many p l a c e s ,  are intergrown.  B i o t i t e i s present as a r u l e .  The t y p i c a l rock would, t h e r e f o r e , seem to have a composition midway between g r a n i t e and quartzdiorite.  To t h i s the name g r a n o d i o r i t e has been applied  also i t may be termed a quartz-monzonite. With an increase o f  the orthoclase and decrease  o f the p l a g i o c l a s e , t y p i c a l g r a n i t e s have been noted, and t . e decrease o f o r t h o c l a s e and increase o f clase and a u g i t e g i v e r i s e to d i o r i t e s . (2) made, i n the A l s h l h l k L<rke d i s t r i c t ,  plagio-  An attempt was  to determine whethe  there was a p r o g r e s s i v e change i n composition across the b a t h o l i t h o r along i t s s t r i k e , but the conclusion was reached that the v a r i a t i o n from the normal type around any s i n g l e l o c a l i t y was g r e a t e r than the v a r i a t i o n exh i b i t e d by the normal type e i t h e r across the b a t h o l i t h or along i t s s t r i k e .  Ko regular change i n the normal  W. E. Sum. and BRp. e l l A.H. Opl (( 1 2 )) C Co o cc k k ff ii e e ll d d W.E. P t . A . P.6A  c1926. it.  (84) type of intrusive was detected, but i t must be remembered that the batholith in this region i s narrow, and possibly no striking change i s to be expected. (1) Caimes describes these rocks as "under the microscope decidedly g r a n o d l o r i t e , " while he describes  (2)  somewhat similar rocks from the Upper White r i v e r  as  commonly diorites but "in addition, granodiorites, quartz granodiorites, g r a n l t i t e s , gabbros, and even homblendites were examined." Where* the b a t h o l i t h i s i n contact ^ i t h the schistose rocks o f the Yukon group, as occurs i n many instances, i t cannot be determined what part of the metamorphlsm o f these rocks i s due to the i n t r u s i o n o f the b a t h o l i t h , and what part i s due to other causes. Along many o f the contacts garnet i s found i n the s c h i s t s , pointing to a c e r t a i n degree o f contact metamorphlsm. Where the limestones o f the schistose group are i n cont a c t with the g r a n i t e s the d e f r e e of contact metamorphlsm i s h i g h ; g a r n e t , e i p d o t o , and other  silicate  minerals are abundant and i n some cases make up the bulk o f the intruded rock, but the zone where these minerals are found i s quite narrow.  I n no instance have  s i l i c a t e minerals been noted more than a quarter o f a (3) mile from the g r a n i t i c c o n t a c t s . (1) Caimes D.D. " A t l i n d i s t r i c t , " G.S.C. Mem. 37, P 58, 1913. ( 2 ) C a i m e s D.D. "Upper White River d i s t r i c t , " G.S.C. Mem 50 p. 95 1915. ( 3 ) C o c k f i e l d W.E.G.S.C. Sum.Rp. P.7A 1926.  (85)  (I) Cockfield found that the western contact of the batho l i t h where observed, i n the Desadeash d i s t r i c t , was steep but the contact minerals show i t to be gently sloping* Pegmatite dykes which are usually contact phenomena have not been reported from the eastern cont a c t but although not common do occur along the western contact.  These pegmatite dykes g e n e r a l l y contain large  crystals of  tourmaline. (2)  Cockfield  has revealed some i n t e r a c t i n g f a c t s  as regards the, Coast Range l n t r u s l v e s . that;  Here he notes  "the presence, on the tops o f many o f the higher  h i l l s , o f bodies o f the intruded rocks, leads to the b e l i e f that these are p o s s i b l y remnants o f the roof of (3) the b a t h o l l t h .  In Whe^ton d i s t r i c t  sever*! long,  re-  l a t i v e l y narrow curtains o f Pre-Jurnseic rocks occur i n the b a t h o l l t h , are cut by the v a l l e y s to depths of 3,000 f e e t or more, and at the l e v e l o f the v a l l e y bottoms are almost as wide as at t h e i r highest In the same d i s t r i c t ,  joints.  small, I r r e g u l a r l y shaped patches  of the o l d e r rocks outcrop at widely d i f f e r e n t e l e v a tions.  These cannot be p o r t s of the r o o f o f the bath-  o l i t h but are i n c l u s i o n s .  The method o f  batholithic  (1) Cockfield G.'^.C. Sum Rn. pprt A 1927 P.6A. (2) Cockfield R'.E G.S.C. Sum.Rp. P. 8A 1926 ( 3 ) Cairnes D.D. "Wheaton d i s t r i c t , " G.S.C. Men. 31, PP 74-76 1912.  (86) invasion which b e s t answers the known f a c t s appears to be that o f overhead stoping — the b a t h o l i t h advancing by the breaking away from the roof o f fragments o r blocks which sank i n the magma that rose to replace them.  The b a t h o l i t h also appears, i n g e n e r a l , to have  intruded the o v e r l y i n g rocks i n the form o f ^reat tongues and dykes, from "hlch branched o f f smaller portions.  However, there in ^ot the minute i n t e r f i n g e r l n g  o f the b a t h o l i t h and the o l d e r rocks that occurs i n connection *vith the Pro-Cambrian b a t h o l i t h s .  There i s  l i t t l e i n the way o f addition o f g r a n i t i c m a t e r i a l t o the intruded rocks, except i n the form o f bodies such as dykes and s i l l s .  distinct  That p c e r t a i n amount  seems e v i d e n t , f o r at the contacts o f seme o f the darker rocks the g r a n i t e becomes darker rs the contact i s approached, but t h i s i s o p e r a t i v e f o r ^ few f e e t o n l y . " i t i s almost c e r t a i n that n cover was maintained over the ^agmp u n t i l i t c o o l e d .  Further,  it  would appear that the r e e f o f the b a t h o l i t h was h i g h l y irregular.  This i s perhaps, be?t i l l u s t r a t e d on the  h i l l s north of Champagne, vhere the submits  of  g r a n i t e and, t h e r e f o r e , r?ct at the r o o f of the b a t h o l i t h ; passing northwird the s ^ - i s t contact a ^e^rr r t a d l s t i n ^ e o f 2 i r l l e s rnd ?t ?n e l e v a t i o n o f Ft l e a s t 2,000 f e e t lower, s t i l l f a r t h e r north^^rd, s c h i s t s are exposed in the b o t t o r of the Mendenhall v s l l e y ; and on  (87) the higher h i l l s to the north o f t h i s v a l l e y g r a n i t e once more appears.  I f i t be assumed that these g r a n i t e  bodies are connected beneath the s c h i s t c o v e r , the o r i g i n a l roof of the b a t h o l l t h must, indeed, have been highly i r r e g u l a r .  Moreover, a study o f the a r e a l geo-  l o g y o f A t l i n to 'Ahitehorse shows that there are numerous o u t l y i n g bodies of g r a n o d i o r i t e thab are i d e n t i c a l I n appearance and composition .vitt the i n t r u s i v e s o f the b a t h o l l t h I t s e l f ,  and no evidence has as y e t been  presented to show thct those ;;rc o f a d i f f e ^ ^ t  age.  They can, perhaps, best be regarded as peaks o f the g r a n i t i c bod^, .hlch have, as y e t , been barely d e r o o f e d . " I t appears to the w r i t e r than i f the Preb s t h c l l t h l c r o d s occur as " c u r t a i n s " as s t a t e d by C o c k f i e l d and i f the g r a n i t i c i n t r u s i v e s have assumed the form of huge tongues cn i n t r u s i o n , these might account f o r the apparent r e g u l a r i t i e s described from C o c k f i e l d above.  I t seems quite p o s s i b l e t h - t these  " c u r t a i n s " could e a s i l y be tuo o r ^cre Jiiles in width or that there could, be a distance oi two, or j o s s i b l y more, miles between the ton^ue3 o f the i n t r u s i v e . C o c k f i e l d i n h i s report on the sar.e d i s t r i c t , has shown that the mincr-1 deposits g i v e some i n d i c a t i o n o f the shape of the b^dy of i n t r u s i v e rocks.  He  f i n d s that there are t.;o ty^es o f m i n e r a l i z a t i o n , namely contact metamor, h i e s.nd hydrothermal.  Con.ta.cb metamor-  (88) phic deposits are b e l i e v e d to have been formed under conditions o f high temperature and pressure, and consequently soon a f t e r the i n t r u s i o n of the b a t h o l i t h . The hydrothermal deposits o f Yukon, belong to deposits formed under conditions of moderate temperature and pressure.  As these occur not only i n the surrounding  rocks, but i n the g r a n o d i o r i t e i t s e l f , i t f o l l o w s that these were formed at a l a t e r d^te than the contact metauiorphic d e p o s i t s , a f t e ^ the up^er part of the g r a r o d l o r i t e had s o l i d i f i e d and c o o l e d . "Moreover, as the mineral deposits o f  this  region occur i n a b e l t f o l l o w i n g the eastern nargin o f the b a t h o l i t h , and as the deposits have been found to be g e n e t i c a l l y connected with tha b a t h o l i t h , i t  follows  that the roc^s to the east of the main boundary ("where most of the Lydrothermal deposits o c c u r " ) are r e a l l y the roof of the b a t h o l i t h .  This i s f u r t h e r borne out by the  f a c t s that numerous o u t l y i n g bodies of g r a n o d i o r i t e occur to the ¿ast o f the main margin o f the i n t r u s i v o s and no evidence has y e t Leen found i n t h i s region that these o u t l y i n ^ bodies d i f f e r i n age from the main i n t r u s i v o s , l b f o l l o w s bhat on the whale the eastern margin o f the b a t h o l i t h i n t h i s region slopes g e n t l y eastward with r e current upward p r o j e c t i o n s ¿¿hose summits have been l a i d bare to the east of the main margin.  This conclusion  —*  ^3  (89)  / (1) not agree with that o f S c h o f i e l d , namely a s t e e p l y dipping and ^mooth*flowing eastern c o n t a c t , with a ,' t narrow ^oat#ct metamorphic zone. / "The deposits o f the contact met amorphic type occur f o ^ the most part at considerable distances from the main margin o f the L a t h o l i t h and are found at the borders o f o u t l y i n g bodies o f g r a n o d i o r i t e .  Deposits  o f t h i s t y p e , with one p o s s i b l e exception, are confined e i t h e r to limestone, schist o r g r a n o d i o r i t e . (2) l o c a l i t y , Jjoeker creek,  At one  a deposit o f t h i s type occurs  i n a s c h i s t i n c l u s i o n , and deposits o f hjdrothermal o r i g i n occur i n the g r a n o d i o r i t e at approximately the same e l e v a t i o n .  As the hydrothermal deposits ^re low  temperature types, compared with^ the contact mctamorphic, and as the d i f f e r e n c e s i n t h i s case c nnot be explained by zoning as o r d i n a r i l y understood, i t ,  therefore,  appears that the time at which the d e p o s i t s were formed becomes the deciding f a c t o r y that deposits formed soon a f t e r the i n t r u s i o n of the b a t h o l i t h were of the contact metamorphic t y p e ; and that near them may be found dep o s i t s of the upper v e i n zone formed i n the dying stages o f vulcanism irom the same i n t r u s i o n . ^ The age o f the Coast Range i n t r u s i v e s has seen, tl)  S c h o f i e l d S . J . and Hanson G. "Salmon River d i s t r i c t , " G.S.C. Mem 132 pp. 64-66 1922. ( 2 ) Cairnes D.D. "Wheaton d i s t r i c t , " G.S.C. Mem 51, PP. 110-111, 140-145 1912.  (90) and s t i l l i s , the source o f many discussions. áfhen (1) C a l m e s f i r s t worked in the Wheaton d i s t r i c t he was o f the opinion that the i n t r u s i v o s antedated the Mesozoic (2) (3) Laberge beds, but h i s l a t e r work i n A t l i n and Wheaton d i s t r i c t s corrected t h i s when he rccognized the f a c t that the g r a n i t e cut the uppermost of the L^berge beds Lnd even the Tantalus conglomerate.  A prominent f e a t u r e  of the Labcrge beds i s con¿_lom.. r - t o s -^hich contain pebbles and boulders of . j y t n i t i c rocks i d e n t i c a l i n character with .the Co.^t Ka^ge i n t r u s i v e s .  Trom t h i s  d - t a Cairnes concluded thut the Coast Range i n t r u s i v e s , although l i t h o l o ^ i c a j - l y very s i ^ i l ^ r , "¿ero intruded at d i f f e r e n t t i ^ e s ; that p^rt& of Lhe b a t h o l i t h v.ere intruded and deroofed to supply m a t e r i a l f o r the Labcrge beds, ¿jid t h a t _ t h i s p e r i o d o f sedimentation w^s f o l l o w e d by further intrusion. Nothing, however, ha? been ^ut forward to show th^t these pebbloa and boulders were a c t u a l l y from the Corst Range b a t h o l i t h , except t h e i r i ' l r ^ i l o r i t y to the i n t r u s i v e s nov.* found. a^e determinations,  lithological  For purposes o f  t h i s evJdcncc i s l a r g e l y  I t i n , t h e r e f o r e , Mere reasonable tc  derived  valueless. the Coast  Range i n t r u s i v e s ir.ith respect only to the rocks they c u t . , I T T Calmes' L.D. "Y.heaton d i s t r i c t ' ' C.&.C7"SeF31, P 53, 1912. ( 2 ) Calmes L.D. " A b l l n d i s t r i c t , " G.L.C. Hen 37,P.59,1913. ( 3 ) C a l m e s D.D. G.S.C. Sum. Rp. 1915 P. 42.  (91) The l a t e r determination o f the age o f the Laberge beds as Lower and e a r l y Middle Jurassic to some extent the age o f the i n t r u s i v e s .  limits  They are  not e a r l i e r than the lower part o f the Middle J u r a s s i c . With regard to the u p ; e r l i m i t o f t h e i r age the evidence i s less certain.  I t has not been d e f i n i t e l y  established  that the Upper Jurassic i s not represented by some part o f the Laberge s e r i e s , and the age of tne Tantalus conglomerate remains i n doubt.  C a i m e s i s o f the opinion  that the Tantalus conglomerates are o l d e r than the intrusives.  He c o r r e l a t e d the Tantnlus conglomerate  with the Kootenay formation o f Lower Cretaceous age (1) found i n northwestern B r i t i s h Columbia.  But Knowlton,  a f t e r examining one c o l l e c t i o n o f f o s s i l plants from the Tantalus, pronounced them t o be Jurasaic.  Thus the  evidence obtained to date i n Yukon i n d i c a t e s that the g r a n i t e i s more recent than the lower part o f the (2) middle Jurassic and o l d e r than c e r t a i n T e r t i a r y rocks.  Beyond  t h i s the age i s not f i x e d . Newer V o l c a n i c s . This includes an important groun o f v o l c a n i c rocks comprising mainly andesites, b a s a l t s , t u f f and breccia and s c o r i a .  anascct^te  These rocks are wide spread  over Yukon and have been reported on from many l o c a l i t i e s . These rocks ^resent, characteristic;; l l y , a b r i g h t (( 1 Cairnes 3 )) C o c k f i e l dD.D. '*.E.  G.S.C. Rp. 1915 G.S.G. Sum. Sum. Rp. 1927  P. P. 41 6A.  *  (92) f r e s h appearance and are contrasted i n t h i s respect with the dominantly d u l l appearing o l d e r v o l c a n i c s p r e v i o u s l y described.  Black, and various shades green and  g r e y , predominate, but reds, ranging from a d u l l b r i c k red o r even purple to b r i g h t v e r m i l l l o n o r even lavender, are by no means r a r e .  Black scoria i s abundant i n the  Ihltehorse d i s t r i c t .  The t u f i s and breccias^ which are  p r e v a i l i n g l y l i g h t e r i n appearance than the l a v a s with vhlch hhcy are IntorbedJod, are g e n e r a l l y ash coloured or  aP.aic ^ol gra^, o r j ^ l l o w . These ¿ x t v - a i v e l ^ v a s aro f o r the g r e a t e r part  p o r p h y r i t i c rock& of medium coarseness, containing pheno c r y c t s o f p l ^ i o c i a s e , hornblende, pyroxene, h i o t i t e and o l i v i n e .  The p l ^ g l c e l a s e f e l d s p a r s range f r o m o l i -  goclase to b y t o j n i t e , but are usually andesine, l a b r a d u r i t e , or bytownite.  Both common green hornblende and  b a s a l t j c hornblende occur. side or hypcr^thene.  The pyroxene i s mostly diop-  The c h i e f a l t e r a t i o n products are  c a l c l t o , e^idot^ ^nd c h l o r i t e . (1) These lav-n i n the dp^er ^hlte River d i s t r i c t cut and o v e r l i e the T e r t i a r y sediments and are thus at le  Joccne i n a^e.  fnese rocks have been studied i n  a number o f l o c a l i t i e s l a Yukon, and wherever d e f i n i t e determinations ¿ould be made they have been assigned to ITT^Cairncs .siiiti River Mem 50. P. 100 1915.  (93) the late T e r t i a r y o r e a r l y P l e i s t o c e n e .  They have been  found to cat the Older Volcanics and the Coast Range i n t r u s i v e s , and are In turn i n t e r s e c t e d by the Acid  (1)  Volcanics.  Mendenhall,  who studied s i m i l a r f l o w s i n  Alaska, says, "These f l o w s , t h e r e f o r e , instead of preceding the deformation o f the e a r l y T e r t i a r y p l a i n , are l a t e r than the d i s s e c t i o n which f o l l o w e d i t s u p l i f t , and are to be regarded as very recent indeed." Whltehorse d i s t r i c t  In  i t i s certain that at l e a s t some o f  the flows have been poured out since the v . H o y s were cut approximately to t h e i r i r e s m t d e j t h s .  This i s  apparent in the c^se o f F i l e s canyon, "rhore Le es r i v e r has cut through a basalt f l c ? i n the v r l l e ¿ to a depth of probably l e s s than 100 f e e t . Acid Volcanics. Grouped under t h i s heading i s a s e r i e s o f rhyol i t e s , quarto-porphyries, g r a n i t e - p o r p h y r i e s , and r e l a t e d rocks with accompanying t u f f s .  latites  These rocks  represent the most recently consolidated roc.is i n Yukon and are of wide occurrence throughout the d i s t r i c t . They occur c h i e f l y as dykes and small rassos. The members o f t h i s group consist of coloured p o r p h y r i t i c rocks ranging f r o u nearly  light .bite,  l i g h t grey or y e l l o w i s h , to pale lavender or d-rker greent l ) Mendenhall ^.C. "The geology of the Úa'n^ral Copper R i v e r Region, Alaska,"U.S.G.s. Prof.Paper 41 PP. 54-62 1905. (<j) Cockfield &Bell A.H.*Whitehorse d i s t r i c t , " G.S.C. Mem. 150. P. 33 1926.  (94) i s h grey shades.  The groundmass i s invariably crypto-  crystalllne and the phenocrysts include mainly f e l d s p a r s , hornblende, and b i o t i t e .  These yoeks have been describ-  ed as rhyolltes, l a t i t e s , quartz-porphyries,  granite-  porphyries andesltes, b a s a l t s , and other v a r i e t i e s have been noted.  They are thought to have been extruded upon  the surface through fissures and necks, but the f i s s u r e s were not open over great distances as these lavas only occur l o c a l l y . (1) Cockfield i s of the opinion that the andesitic and b a s a l t i c flows are older than the more acid v a r i e t (2) i e s . Caimes, in the Wheaton d i s t r i c t , observed volcanic necks, surface flows, and tuffaceous accumulations in their characteristic forms and concluded that these rocks were of comparatively late o r i g i n , and assigned them to the late Tertiary or Pleistocene. In the Mayo h i l l (3) (4) d i s t r i c t , Stockwell and Cockfield in the Aishihlk Lake d i s t r i c t consider that these rhyolltes and quartz-porphyries  are connected with the granitic rocks.  These  Acid Volcanics cut the Newer Volcanies wherever they come in contact with them and are thus younger than the Newer (5) Volcanies. In the Up.er White River d i s t r i c t Caimes (1) Cockfield W.B. G.S.C. Sum. Rp. 19H2 P.6A. (2) Caimes D.D. "Wheaton d i s t r i c t , " G.S.C. Mem 31, P. 60-76 1912. ( 3 ) Stockwell G.S.C. Sum. Rp. 1925 P.A. (4) Cockfield W.E. G.S.C. Sum. Rp. 1926 P.A. (5) Caimes D.D. "Upper White River d i s t r i c t , " G.S.C. 50 P.101 1915.  (95)  shows that these rocks have flowed over the present land surface since i t has become u p l i f t e d and eroded to nearly i t s present form, the topographic features having since been modified only by g l a c i a t i o n . are thus of l a t e Tertiary o r Pleistocene age.  .3  UBC Scanned by UBC Library  They  (96)  ECONOMIC  GEOLOGY.  The economic aspect of geology i n Yukon i s not very favourable.  I n the f i r s t place prospecting i s e x -  ceedingly d i f f i c u l t due to the thickness o f the d r i f t and the overburden.  In the seeond p l a c e , Yukon i s  rather  remotely s i t u a t e d and thus the cost o f production i s g r e a t l y increased by the transportation charges. Although the climate o f the region i s not as severe as considered by most people i t i s severe enough t o prevent operations f o r approximately seven months, however, the long_days I n the summer months r e a d i l y ?ermit surface work without the use o f a r t i f i c i a l  lights.  The mineral deposits consist o f  practically  only two t y p e s , namely, contact metamorphic deposits and f i s s u r e vein-replacement d e p o s i t s .  The l a t t e r  is  d i v i s i b l e i n t o three d i v i s i o n s and w i l l be d e a l t with in detail  later. The contact metamorphic deposits contain c h i e f -  l y copper values with t r a c e s o f g o l d i n some p l a c e s . They occur as i r r e g u l a r masses without any d e f i n i t e trend.  They occur i n two c o n d i t i o n s ; f i r s t i n a l t e r e d  limestone c l o s e „to o r i n d i r e c t contact with the Coast Ranfie i n t r u s l v e s , and secondly, they occur i n the s c h i s tose rocks at the contact with the same i n t r u s l v e s .  Cockfleld  s t a t e s , " There can be no doubt about the  close genetic connection between the ore-bodies and the intrusion of the Coast Range batholith, this connection being apparent even on most casual examination."  The  minerals are chalcopyrite, bornite, tetrohedrite,  chal-  cocite and their oxidation products, malachite, chrysocolla, cuprite and malaconite.  azurite,  The cuprite i s  occasionally associated with native copper. Pyrrhotite and pyrite are not abundant but magnetite and hematite occur in large masses.  The ores have either a gangue of  magnetite and hematite or a gangue of s i l i c a t e minerals. The g o l d - s i l v e r veins are typically high temperature deposits in the intruded rocks and in the granite itself.  The gold occurs in the f r e e state and i s intim-  ately associated with the s u l f i d e s , pyrite and pyrrhotite. These deposits are of considerable importance as the sourees of the placer gold of Yukon but not at present of any great economic value. The s i l v e r - l e a d veins represent the mining wealth of Yukon.  These veins are subdivided into three  (2)  groups on a mlneralogical b a s i s . In the f i r s t group galena and f r i e b e r g i t e are the chief ore minerals and manganiferous s i d e r i t e i s the chief gangue mineral. small quantities.  Quartz and pyrite are present in  Cerusslte, limonite and manganite are  ((2) 1 ) Stockwell Cockfield W.E. G.S.C. G.S.C. Sum. Sum. Rp. Rp. 1922 1925 Pt.A. Pt.A.  (98) oxidation products; chalcopyrite, malachite and azurite are present in small amounts.  These veins are high in  s i l v e r values with no gold values.  They represent the  best mineralization type of vein in Yukon. The second group of veins have a gangue of quartz or ankerite, calcite in a few places, and sider i t e either subordinate or absent* contains manganese.  The ankerite usually  Galena, f r i e b e r g l t e and zinc-blende  are the ore minerals; pyrite, limonita, cerussite, copyrlte, malchite and azurite are also present.  chalIn  these veins the s i l v e r content i s important although small values f o r gold are obtained.  This group of veins  and the group described immediately above belong to the transverse veins which w i l l be described l a t e r . The quartz-arsenopyrite veins represent the third group.  Quartz i s the chief gangue mineral but  ankerite, calcite and s e r i c i t e are present.  Arsenopyrite  i s characteristic and pyrite, galena, zinc-blende and pyrrhotite occur also.  Native gold has been found in  these veins, but like the s i l v e r values, i s low. site^ and limonite occur as oxidation products.  CerusDeposits  of this type belong to the longitudinal c l a s s , as described below, and are not as yet of any importance.  (1)  (2)  Cockfield and Stockwell have described the lead( 1 ) Cockfield ^.E. ( 2 ) Stockwell  G.S.C. Sum. Rp. 1923. P t r U l G.S.C. Sum. Rp. 1925 Pt.A.  (99) s i l v e r veins in some d e t a i l i n the Mayo d i s t r i c t . they found that the ore deposits are p r a c t i c a l l y  Here all  f i s s u r e v e i n s , that i s , they represent v e i n m a t e r i a l deposited i n f a u l t f i s s u r e s .  The f a u l t s are a l l normal  f a u l t s with a h o r i z o n t a l displacement o f 500 f e e t o r more.  The l o n g i t u d i n a l and transverse f a u l t s occur and  are determined mainly by t h e i r m i n e r a l i z a t i o n .  The  transverse f a u l t i n g , that c u t t i n g across the bedding, i s a t t r i b u t e d to the bending o f the beds from an e a s t west d i r e c t i o n to a southerly d i r e c t i o n and they trend o ó N. 5 W t o N. 15 E. The l o n g i t u d i n a l f a u l t s , those p a r a l l e l l i n g the s t r i k e o f the beds, may be due t o the s t r e s s e s developed at the time o f the i n t r u s i o n o f the o o g r a n i t i c masses and trend N. 30 -40 E. The e a r l i e r m i n e r a l i z a t i o n , i n the l o n g i t u d i n a l f a u l t s , consists o f quartz, arsenopyrite and p y r i t e * These l o n g i t u d i n a l f i s s u r e s remained planes o f weakness, after f i l l i n g ,  and were a f f e c t e d by subsequent movement.  The transverse f i s s u r e s acted as c i r c u l a t i o n channels f o r the m i n e r a l i z e r s and considerable amounts o f minerals were deposited i n them.  Thus, the p r i n c i p a l Ore shoots  are found i n the transverse f i s s u r e s .  The c h i e f minerals  o f these f i s s u r e s are galena, s i d e r i t e  (manganiferous)  f r e i b e r g i t e and s p h a l e r i t e . Both the gentlemen previously mentioned noted a ruj.e:- "Where the transverse f a u l t taps a l o n g i t u d i n a l  (100) f a u l t and passes upward out of a hard stratum, such as quartzlte or greenstone, into schist, an ore-shoot i s usually found in the vein beneath the schist as i f the l a t t e r had acted as an impervious b a r r i e r to the orebearing solutions and had forced deposition at that (1) point."  Stockwell  states, "This i s probably due to  the f a c t that the f i s s u r e through the harder rocks r e mained open to the ore-bearing solutions, whereas in the schist the f a u l t was more or less sealed by a clayey impervious gouge, forming a dam which forced(2)deposition below i t . " the l a t t e r .  Evidence i s offered by Cockfleld  to prove  The transverse fissures are short and are  not l i k e l y to continue with depth but there i s always the p o s s i b i l i t y of finding ore-bodies i n them.  The  schist however i s not barren of ore in a l l cases. The mineralogy of the veins i s interesting as i t affords some l i g h t on the occurrence of the s i l v e r . Native elements. Sulfides.  Sulpho-salts Oxides Carbonates Sulphates. t l ) Stockwell (2) Cockfleld W.E.  s i l v e r , gold. argentite, galena, sphalerite, c o v e l l i t e , chalcopyrite, pyrite and arsenopyrite. pyrargyrite, f r e i b e r g i t e , polybaslte, jamesonite. — quartz, llmonlte, manganlte. siderite, calcite, cerussite, malachite, azurite. barite. Op. c i t . Op. c i t .  MS ' -.^ (101)t Argentite*  -  this mineral i s uncommon bat l a found in small masses enclosed in cerussite and as crystals with galena.  Salena  - this I s the most important mineral and i s found i n nearly every deposit. I t i s commonly coarsely crystalline and i s not intimately intergrown with the other ore or gangue minerals* The coarse galena has a rather gneiasoid appearance* The fine-grained steel galena l a rare but carries average values i n s i l v e r *  Sphalerite - - - occurs i n most of the deposits* I t i s generally yellowish brown and resinous in appearance. Covellite  —  ChalcopyritePyrite  i s very r a r e . i s not common and where found i s , as a r u l e , intimately associated with galena.  —- l a f a i r l y abundant and occurs both with arsenopyrite and galena.  Arsene pyrites- occurs with quartz and pyrite i n the veins of the older s e r i e s . Pyrorgyrite  i s r a r e . I t occurs with f e i b e r g i t e and galena and was noted i n only a few deposits where i t i s of l o c a l occurrence and not disseminated.  Freibergite — i s common and i s one of the chief s i l v e r minerals. Where f r e i b e r g i t e i s present even i n small quantities the s i l v e r value of the ore l a increased. This mineral i a associated with s i d e r i t e , galena and sphalerite. Polybasite  i s of rare occurrence* be secondary*  Jamesonite  also r a r e . I t may belong to the quartzarsenopyrite stage of mineralization.  Quartz  I t i s believed to  (102) Limonite and Manganite.  these are oxidation products. The l a t t e r l a believed to have been derived from the aider!te*  Siderlte or Mangano-alderlte. this i s the moat abundant gangue mineral. The colour varies from dark brown to l i g h t brown in depth* I t l a as a whole f i n e l y c r y s t a l l i n e , bat many eoaraely c r y s t a l l i n e masses were found. This mineral i a always accompanied by f r e i b e r g l t e , galena and sphalerite. Calcite  i a not common and i s mostly associated with a i d e r l t e .  Cercasite  ia confined to the surface and i s not common* I t occurs as white earthy masses*  Malachite and Azurlte --occur as oxidation products. Borite  —  i a of rare occurrence and ia a gangue mineral*  The majority of the veins represent a simple f i l l i n g of f a u l t fissures*  Replacement of the wall rock  operated only to a alight extent.  The ore minerals are  i n most cases fastened to the polished walls and do net (1) project into them.  I t i s believed  that the small open-  ings of the f a u l t s increased as mineralisation took place.  I t i s possible that the c r y s t a l l i z i n g force of  the minerals may have assisted the widening of the fissures*  Seme replacement i s noted in the Sadie-  Treadwell vein of Kens B i l l * (1) d o c M i e l d W.K.  d . S . C . Sum* Rp.  1365  A.  (110)  (1) Cockfield  found that the acid dyke rocks, in  the Keno H i l l area, carry small amounts of galena, pyrite and tetrahedrite.  These are not considered as  the source of the mineralizing solutions but i t i s b e lieved that the solutions and the acid dykes have been derived from a l a r g e r body of magma.  Granitic rocks  occur in the vicinity of nearly a l l the ore deposits and I t i s possible that these o u t l i e r s represent peaks of a batholith that underlies the area.  The age of the  granite i s not d e f i n i t e l y fixed but the ore deposits are younger than the granite, and beyond this their age cannot be f i x e d more d e f i n i t e l y . Secondary enrichment i s practically unknown in glaciated areas but occurs at the St, Eugene, Premier and Dolly Varden mines of B r i t i s h Columbia,  In the  workings at Keno H i l l area, the f r o s t extended down to the 350 foot l e v e l so any secondary enrichment found i n this region i s considered to antedote g l a c i a t l o n .  The  f r o s t i s believed to have originated in the Pleistocene Period.  The geological evidence and mineralogical com-  position of the main (2)ore-bodies point to a primary origin and Cockfield  i s of the opinion that secondary  enrichment played a r e l a t i v e l y minor role i n the form_ ation of these deposits. (1) Cockfield W.E+ ( 2 ) Cockfield W.E.  G.S.C. Sum. Rp.  Op. c l t . 1923 Pt. A.  (104) The silver-antimony veins have a quartz gangue.  They carry low values in s i l v e r and their  origin i s considered the same as the veins above. A l l these l e a d - s i l v e r and silver-antimony vein deposits are believed to have been formed at moderate depths by hot ascending solutions.  I t i s also consider-  ed that the mineralizing solutions had their origin i n the same magma that gave r i s e to the acid dykes and s i l l s , a n d that the changes in ore with depth w i l l depend upon changes in primary deposition. Cockfield notes,  I t may also be pointed out  that the majority of the ore-bodies occur in connection with outlying bodies of granite rather than with the main mass of the batholith, although there are many exceptions.  I t may also be l a i d down as a general rule  that the main mass of the batholith away from i t s borders i s not l i k e l y to have been the seat of ore deposition, except possible where there are inclusions of the older intruded rocks." These mineral deposits are i n many ways similar to the ore deposits of B r i t i s h Columbia. metamorphic deposits are i d e n t i c a l .  The contact  The l e a d - s i l v e r  veins resemble those of the Slocan d i s t r i c t and those of the I n t e r i o r Plateau region of B r i t i s h Columbia. ( 1 ) Cockfield W.E.  The  G.S.C. Sum. Rp. 1922 Pt.A.  (135) s t r i k i n g f e a t u r e o f the l a t t e r i s the f a c t that the s i l v e r values l i k e those o f Yukon are i n t i m a t e l y assoeia ted with t e t r a h e d r l t e and f r e l b e r g i t e . i n Yukon and i n B r i t i s h Columbia that i f  I t i s found both tetrahedrlte  or f r e l b e r g i t e are both absent from a deposit the s i l v e r values are low.  I n Yukon the s i l v e r has proved to be  uniformly d i s t r i b u t e d through the galena when f r e e from gangue.  The average s i l v e r value f o r the area i s 200  ounces per t o n .  I t i s known that s i l v e r may e x i s t i n  galena i n the form o f sub-microscopic p a r t i c l e s o r i n s o l u t i o n only up t o 0.2 per c e n t .  Under the microscope  the galena from Keno H i l l area shows c r y s t a l s o f argent i t e and f r e l b e r g i t e intergrown with the g a l e n a . Saline i n c r u s t a t i o n s occur at many points (1) along the Dezadeash R i v e r v a l l e y and a l s o along A i s h i h l k river.  This m a t e r i a l i s white and occurs around the  edges o f lakes and small ponds, being l e f t as a residue a f t e r the evaporation o f the water.  These s a l i n e en-  crustations also occur a t many p o i n t s as a thin d e p o s i t on top o f the s o i l .  I n some of these cases there i s  apparently an abundance of stagnant water e a r l y i n the spring, and the encrustations are l e f t as the water evaporates,  They contain hydrated sulphates o f limo  and soda, with a small quantity o f magnesium sulphate, ( 1 ) C o c k f i e l d W.E.  G.S.C. Sum. Rp.  1923  P t . A.  (106) and insoluble argillaceous and organic matter.  They  are s l i g h t l y ferrugenous and contain small quantities of chlorides and phosphates.  The potassium content i s  0.2 to 0+5 per cent K^O. Coal* The coal-bearing formations of Yukon are a l l of either Tertiary or Jura-Cretaceous age.  The mineral  f u e l s in the Tertiary beds are c l a s s i f i e d as l i g n i t e s , while those of Jura-Cretaceous age range from highgrade l i g n i t e to anthracite. The Tertiary coal beds are not of very great areal extent, but have a wide d i s t r i b u t i o n .  In places  these beds apparently constitute remnants of once l a r g e r areas now Infolded with older terranes, but in most cases they represent deposits l a i d down in separate basins of deposition.  The f o s s i l plant remains show  that most of them are of fresh-water o r i g i n ,  These beds  are correlated with the Kenai series which i s generally referred to the upper Eocene.  These rocks are In most  places l i t t l e disturbed, although l o c a l l y they have suffered considerable deformation.  The rocks of the  Kenai series consist of l i g h t coloured conglomerates and sandstones and light and dark shales an? c l a y s . Volcanic material i s also associated with these sediments in seme places. The coal of Tertiary age i s c l a s s i f i e d as l i g n i t e  (107) (1)  and Cockfield  states that;  "These deposits have  BO present economic importance, f o r other deposits of a much better grade at Tantalus are capable of supplying requirements f o r many years to come*" The Tertiary coals have been mined at only three points; 1. C l i f f Creek; 2. Coal creek (tributary of Yukon r i v e r ; ) 5* Coal creek (tributary of Rock creek.) The known areas of Tertiary coal beds cover a t o t a l of 1,450 square miles with this much area again as a favourable coal horizon.  The estimated tonnage of the known  coal areas i s 4,690,000,000. metric tons. The period of Tertiary coal deposition of Yukon probably corresponds with the period of Tertiary coal deposition known in British Columbia to the south. The coal seams of Jura-Cretaceous age are closely associated with the Tantalus conglomerate beds.  Two  horizons have been recognized — an upper horizon occurring near the top of the Tantalus conglomerate, to which belong the seams at Ishe Tantalus mine; and a lower h o r i zon some distance below the conglomerate which contains the seams at the Five Finger mine, These coal bearing beds have been much mere disturbed than those o f Tertiary age*  These Jura-Cretac-  eous beds are considered as remnants of former extensive (1)  C o c k f i e l d i.Ji  " S i x t y r i l e and L^due R i v e r s , " C.C.S. 3921.  (108) areas which were o r i g i n a l l y a l l connected but have been reduced by erosion to their present proportion.  (1) Caimos  In considering the distribution of the coal i s of the opinion that, in a general way, i t  i s c h i e f l y to be found in the areas covered by the Tantalus conglomerate*  Farther he declares, i t would  be quite possible f o r coal seams of the lower horizon to be found where the overlying conglomerate was not to bo seen, being either covered by other formations or deposits, or,having been eroded away.  In only one  l o c a l i t y namely, at the Five Fingers mine have coal seams of any economic value been found where the Tantalus conglomerates are not in evidence.  In any  ease, Cairnes states, the Coal Measures of the upper horizon contain much the more valuable coal seams.  In  a l l geological and prospecting work these conglomerates form a very valuable horizon marker, which i s very readi l y i d e n t i f i e d , and, when found, the approximate p o s i t ions of both coal horizons can be determined at once. The thickness of the coal seams of the Tantalus beds varies from eighteen inches up to eight f e e t . (2)The coal on a whole i s classed as low carbon bituminous although individual outcrops vary from l i g n i t e to anthracite. (1) Cairnes D.D. "Lewes and Rivers," G.S.C.Fields MemNordenskiold 5,of P.Canada," 48 1910. (2) Cowling D.B. "Coal G.S.C. Mem.59, P. 150, 1915.  (109) The only coal mine working these c o a l s i s the Tantalus mine.  Here the c o a l outcrops i n three seams  on the r i v e r banks and i s , t h e r e f o r e , w e l l situated f o r economical working*  The three seams have been opened  u p , but only the lower two have been worked t o any extent.  The seams are somewhat v a r i a b l e i n width but  have averaged 7 * 6 * * , 6*6'* and three f e e t o f c o a l i n the bottom, middle and top seams r e s p e c t i v e l y .  The low-  e r two seams have i n places not nore than f o u r f e e t o f rock between them, and the middle and top seams are o g e n e r a l l y reven f e e t a p a r t .  The seams dip from 24 t o 40  and are somewhat d i r t y but the eoal could e a s i l y be washed and s t o r e d . An average analysis o f the seams shows the following  results:-  Water V o l a t i l e combustible master Fixed Carbon Ash  0.75 0.82 25.61 - 25.12 55.21 - 66.05 20.45 8.05 IS535S  Firm coherent coke per eent  75.64 - 74.06  The demand f o r coal i n t h i s region i s small and i t i s used mainly f o r f u e l i n g some o f the r i v e r b o a t s . A c c e s s i b l e wood, near the r i v e r s , used f o r f u e l i n g the steamers i s r a p i d l y decreasing and e i t h e r c o a l o r o i l w i l l be required as f u e l i n the f u t u r e .  o  (ii) BIBLIOGRAPHY.  Brooks, A.H. 1* "The Geography and Geology o f A l a s k a . " United States G e o l o g i c a l Survey. P r o f e s s i o n a l paper NO.45, 1916. 2+ "A reconnaissance from Pyramid Harbor to Eagle City, Alaska." United States G e o l o g i c a l Survey. 21st Annual Report Part I I . 1899 - 1900. Brooks, A.H. and K i n d l e , E.M. 1 . " P a l a e o z o i c an^ associated rocks o f the Upper Yukon, Alaska.* B u l l e t i n G e o l o g i c a l S o c i e t y of America Volume XIX, 1908. Pages 264 - 271. C a i m e s , D.D. 1. "Report on a p o r t i o n of the Conrad and Whitehorse' Mining D i s t r i c t s , Yukon." G e o l o g i c a l Survey o f Canada. No. 982B 1908. 2 . "Explorations i n a p o r t i o n o f the Yukon south o f Whltehorse." C,G.S. Sum. Rp. 1906 Pages 22 - 30. 5 . "Recent developements i n mining i n the southern Yukon. Can. Min. Jour. 2 8 ( n . s l ) pages 87-88, 121 - 122, 1907. 4. "Preliminary memoir on the Lewes and NordenskiSld Rivers Coal D i s t r i c t , Yukon T e r r i t o r y . " G e o l o g i c a l Survey o f Canada Memoir 5 , 1910. 5. "Wheaton D i s t r i c t , Yukon." G e o l o g i c a l Survey o f Canada Memoir 51, 1912. 6. "The Yukon - Alaska I n t e r n a t i o n a l Boundary between Porcupine and Yukon R i v e r s . * G e o l o g i c a l Survey o f Canada Memoir 67, 1914. 7 . "Upper White R i v e r D i s t r i c t . " G e o l o g i c a l Survey o f Canada. M w o i r 50, 1915. 8 . " P o r t i o n s of the A t l i n Mining D i s t r i c t , B r i t i s h Columbia." G e o l o g i c a l Survey o f Canada. Memoir 57, 1913. 9 . " S c r o g g i e , Barker, T h i s t l e and Kirkmon Creeks. G e o l o g i c a l Survey o f Canada. Memoir 97, 1917. 10. "Explorations i n Southern Yukon." G e o l o g i c a l Survey o f Canada, Summary Report, 1914. Pages 10 - 33. 11. "Whitehorse and Tantalus A r e a s . " G e o l o g i c a l Survey o f Canada. Summary Report, 1908. Pages 26 - 28.  (iii) 12. "Mayo Area: and Scroggie, Barker, Thistle and Kirkman greeks; and Wheaton D i s t r i c t . 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"The Mayo S i l v e r - L e a d D i s t r i c t , Yukon." Can. Min. Jour. Vol 45, No 37, Page 891 - 893, Sept. 12, 1924. Min. Mag. V o l . 30, No. 2 Pages 122 - 123 Feb. 1924.  (cxx) Coekfield W.E. 16* "Upper Beaver River Area, Yukon." G.S.C. Sum.Rp. 1924, Pt. A. 17* "Alshihik Lake D i s t r i c t , Yukon." 8+8.C. Sum. Rp. 1926, Pt. A. 18  "Silver-Lead Deposits of Rude Creek, Yukon." G.S.C. Sum.Rp. 1927. Pt. A.  19  "Dezadeash Lake Area." G.S.C* Sum. Rp. 1927  20  "Silver-Lead Deposit of Fifteen Mile Creek, Yukon." G.S.C. Sum.Rp. 1927 Pt. A.  21  "Pueblo, Tamarack-Carlisle and War-Eagle-Le Roi Properties, Yukon." G.S.C. Sum.Rp. 1927 Pt.A.  22  " L i t t l e Salmon Area, Yukon." G.S.C. Sum.Rp. 1928 Pt. A.  Pt. A.  Ceckfield W.E. and B e l l A.H. 1 "Whitehorse D i s t r i c t , Yukon." G.S.C. Memoir 150, 1926. C o l l i e r , A.J. 1. "The Coal Resources of Yukon, Alaska." U.S.G.S. B u l l . 218, 190S. Dali W.E. and Harris G.B. 1. "Correlation Papers.* U.S.G.S. B u l l . 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